• Line a 9-by-13-inch baking dish with foil, leaving a 2-inch overhang on two sides; coat the foil with cooking spray. Preheat the oven to 350 degrees F (unless making no-bake bars, Nos. 44 through 50).
• Prepare your batter or dough. Spread in the prepared pan or press in using damp or oiled fingers.
• Bake as directed, then transfer to a rack and let cool completely in the pan. 

1. Chocolate Chip Cookie Bars Beat 2 sticks softened butter and 1 cup each granulated and light brown sugar with a mixer on medium-high speed until fluffy; add 3 eggs and 1 1/2 teaspoons vanilla. Reduce the speed to low. Add 3 cups flour and 3/4 teaspoon each baking soda and salt; beat until combined. Stir in one 12-ounce bag chocolate chips. Bake until a toothpick inserted into the center comes out clean, 35 to 40 minutes.

2. M&M Bars Make Chocolate Chip Cookie Bars (No. 1), replacing the chocolate chips with 1 1/2 cups M&M's and 1 cup mini chocolate chips.

3. White Chocolate–Macadamia Nut Bars Make Chocolate Chip Cookie Bars (No. 1), using 1 tablespoon vanilla and replacing the chocolate chips with 1 cup each white chocolate chips and crushed salted macadamia nuts. 

4. Glazed Cappuccino Bars Make Chocolate Chip Cookie Bars (No. 1), adding 2 tablespoons instant espresso powder with the butter. For the glaze, whisk 1 cup confectioners' sugar with 1 to 2 tablespoons hot water and 1/2 teaspoon vanilla until smooth; drizzle over the cooled bars. 

5. Maple-Cinnamon Bars Make Chocolate Chip Cookie Bars (No. 1), replacing 1/2 cup of the brown sugar with pure maple syrup. Add 1/4 teaspoon maple extract with the vanilla and replace the chocolate chips with one 10-ounce bag cinnamon baking chips.

6. Banana-Chocolate Bars Make Chocolate Chip Cookie Bars (No. 1), adding 1 mashed large overripe banana with the eggs; omit the baking soda and chocolate chips. Dollop 1/2 cup chocolate-hazelnut spread onto the batter in the pan and swirl. Bake 30 to 35 minutes.

7. Chocolate-Mint Bars Make Chocolate Chip Cookie Bars (No. 1), replacing the chocolate chips with crushed chocolate-mint sandwich cookies. 

8. Cherry–Chocolate Chunk Bars Make Chocolate Chip Cookie Bars (No. 1), adding 1/4 teaspoon almond extract with the vanilla and replacing the chocolate chips with 1 1/4 cups each chocolate chunks and chopped dried cherries.

9. Sugar Cookie Bars Melt 2 sticks butter; let cool slightly. Whisk in 1 1/2 cups sugar, 3 eggs and 1 tablespoon vanilla. Stir in 2 cups flour and 1/4 teaspoon salt. Bake until the edges are set but the center is soft, about 25 minutes. 

10. Birthday Cake Bars Make Sugar Cookie Bars (No. 9); fold 1/2 cup rainbow sprinkles into the batter before baking. Spread vanilla frosting over the cooled bars; top with more sprinkles. 

11. Snickerdoodle Bars Make Sugar Cookie Bars (No. 9), adding 1 1/2 teaspoons cream of tartar with the flour. Sprinkle with 1/4 cup cinnamon sugar before baking. 

12. Apple Pie Bars Saute 2 diced peeled Golden Delicious apples in 1/2 stick butter with 1 tablespoon sugar and 1 teaspoon apple pie spice until softened. Make Sugar Cookie Bars (No. 9), stirring the apples into the batter. Sprinkle with coarse sugar before baking.

13. Chai Tea Bars Make Sugar Cookie Bars (No. 9), adding the contents of 2 chai tea bags with the flour. For the glaze, whisk 1 cup confectioners' sugar with 1 to 2 tablespoons hot brewed chai tea and 1/2 teaspoon vanilla until smooth; drizzle over the cooled bars. 

14. Ginger-Molasses Bars Make Sugar Cookie Bars (No. 9), using only 1/2 cup granulated sugar and adding 1/2 cup each light brown sugar and molasses; add 1 teaspoon ground ginger with the flour. Sprinkle with chopped crystallized ginger before baking.

15. Oatmeal-Raisin Cookie Bars Pulse 2 sticks softened butter with 3/4 cup each granulated sugar and brown sugar in a food processor until combined. Add 2 1/2 cups rolled oats, 1 1/2 cups flour and 1 teaspoon each baking powder and salt; pulse to combine. Add 2 cups raisins, 2 eggs and 2 teaspoons vanilla; pulse until large clumps form. Bake until the edges are set but the center is soft, about 35 minutes. 

16. Oatmeal-Fig Bars Make Oatmeal-Raisin Cookie Bars (No. 15), replacing 3/4 cup of the all-purpose flour with whole-wheat flour and the raisins with chopped dried figs.

17. Oatmeal Shortbread Bars Mix 2 cups flour with 1 1/2 cups rolled oats, 1 cup confectioners' sugar, 1 teaspoon baking powder and 1/2 teaspoon salt. Work in 3 sticks softened butter with your fingers until large clumps form. Bake until lightly browned, 30 minutes. 

18. Linzer Shortbread Bars Make Oatmeal Shortbread Bars (No. 17), replacing the oats with 3/4 cup almond flour and using only 2 sticks butter. Press two-thirds of the dough into the prepared pan; spread with 1 1/4 cups seedless jam and crumble the remaining dough over the top. Bake until lightly browned, 40 to 45 minutes. 

19. Pumpkin Spice Bars Make Oatmeal Shortbread Bars (No. 17), using 2 1/2 cups flour and adding 1 1/2 teaspoons pumpkin pie spice with the flour. Press three-quarters of the dough into the prepared pan; spread with 1 1/2 cups pumpkin butter and crumble the remaining dough over the top. Bake until lightly browned, 40 to 45 minutes. 

20. Pecan Pie Bars Mix 3 cups finely ground vanilla wafers with 1/4 cup granulated sugar and 1 1/2 sticks melted butter. Press into the prepared pan; bake 10 minutes. Let cool completely. Whisk 1 cup light corn syrup with 1/2 cup brown sugar, 1/2 stick melted butter, 3 eggs, 1 teaspoon vanilla and a pinch of salt; pour over the crust and top with 2 cups roughly chopped pecans. Bake until the edges are set but the center is still loose, 25 to 30 minutes. Let cool, then chill until set. 

21. Cheesecake Bars Mix 3 cups finely ground graham crackers with 1/4 cup sugar and 1 1/2 sticks melted butter. Press into the prepared pan; bake 10 minutes. Let cool completely. Beat 24 ounces softened cream cheese with 1 cup sugar until smooth. Beat in 2 eggs, 1/4 cup sour cream and 1 teaspoon vanilla. Spread over the crust; bake until the edges are set but the center is still loose, about 30 minutes. Let cool, then chill until set. 

22. Strawberry Cheesecake Bars Make Cheesecake Bars (No. 21), using chocolate graham crackers for the crust. Swirl 1/3 cup warmed strawberry jam into the batter in the pan before baking. 

23. Key Lime Cheesecake Bars Bake the crust for Cheesecake Bars (No. 21). For the filling, beat 8 ounces softened cream cheese with 2 eggs until smooth. Beat in one 14-ounce can sweetened condensed milk and 2/3 cup Key lime juice. Bake only 25 minutes.

24. Lemon Bars Mix 2 cups flour with 3/4 cup confectioners' sugar and a pinch of salt; work in 2 sticks softened butter with your fingers until large clumps form. Press into the prepared pan; bake until lightly browned, 20 to 25 minutes. Let cool 5 minutes. Whisk 5 eggs with 1 1/2 cups sugar, 1 cup lemon juice and 1/3 cup flour until smooth; pour over the crust. Bake until set, 20 to 25 minutes. Dust the cooled bars with confectioners' sugar. 

25. Lavender Lemon Bars Make Lemon Bars (No. 24), adding 1 teaspoon each grated lemon zest and ground dried lavender with the flour for the crust.

26. Red Currant Lemon Bars Make Lemon Bars (No. 24), adding 1/2 cup warmed red currant jelly with the eggs.

27. Orange Bars Make Lemon Bars (No. 24), using only 2 tablespoons lemon juice and adding 1 cup orange juice and 2 teaspoons vanilla with the eggs. 

28. Classic Brownies Melt 2 sticks butter with 4 ounces chopped semisweet chocolate; let cool slightly. Stir in 2 cups sugar and 4 eggs. Whisk in 1 1/2 cups flour, 1/3 cup unsweetened cocoa powder and 1/2 teaspoon salt. Bake until a toothpick inserted into the center comes out clean, 30 to 35 minutes.

29. Coconut Brownies Whisk 3 egg whites with 1/2 cup sugar and 1/2 teaspoon salt; fold in one 7-ounce bag shredded sweetened coconut. Make Classic Brownies (No. 28); sprinkle the coconut mixture over the batter in the pan. Bake until lightly browned, about 1 hour. 

30. Chocolate-Hazelnut Brownies Make Classic Brownies (No. 28); stir 3/4 cup crushed hazelnuts into the batter before baking. For the frosting, beat 1 cup chocolate-hazelnut spread with 1/2 stick softened butter and 2 tablespoons milk; spread over the cooled brownies. Top with hazelnuts. 

31. Peanut Butter Cup Brownies Make Classic Brownies (No. 28); press 16 chocolate–peanut butter cups into the batter in the pan before baking. 

32. Health Nut Brownies Make Classic Brownies (No. 28), replacing 1 stick butter with 1/2 cup coconut oil and the cocoa powder with chocolate protein powder. Stir 1/4 cup each chia seeds and chopped walnuts into the batter before baking.

33. Marble Brownies Beat 12 ounces softened cream cheese, 1/3 cup sugar and 1 egg until smooth. Make Classic Brownies (No. 28); swirl the cream cheese mixture into the batter in the pan. Bake 35 to 40 minutes. 

34. Classic Blondies Melt 2 sticks butter; let cool slightly. Whisk in 2 cups light brown sugar, 2 eggs and 1 tablespoon vanilla. Stir in 2 1/2 cups flour and 1/4 teaspoon each baking soda and salt. Fold in 1 1/2 cups butterscotch chips. Bake until a toothpick inserted into the center comes out clean, 30 to 35 minutes.

35. Butterscotch Pretzel Bars Make Classic Blondies (No. 34); swirl 1/2 cup butterscotch caramel sauce into the batter in the pan, then sprinkle with 1 cup broken pretzel sticks before baking. 

36. Blueberry Coffee Cake Bars Mix 1 cup each flour and light brown sugar, 1/2 cup rolled oats and 1/4 teaspoon salt; cut in 1 stick cold cubed butter with a fork until large clumps form. Make Classic Blondies (No. 34), adding 1/2 teaspoon cinnamon with the flour; replace the butterscotch chips with blueberries. Top the batter in the pan with the crumb mixture, then bake until the edges are set and the center is firm, about 40 minutes. Dust the cooled bars with confectioners' sugar. 

37. Triple-Decker Bars Make Classic Brownie batter (No. 28) and Classic Blondie batter (No. 34). Spread the brownie batter in the prepared pan; press chocolate sandwich cookies into the top. Spread the blondie batter over the cookies. Bake until a toothpick inserted into the center comes out clean, 50 to 55 minutes. 

38. Gluten-Free Peanut Butter–Chocolate Bars Beat 3 cups creamy peanut butter with 2 cups sugar, 3 eggs, 2 teaspoons vanilla and 1 teaspoon salt until smooth. Bake until a toothpick inserted into the center comes out clean, 30 to 35 minutes. Pour 1/2 cup warmed heavy cream over 6 ounces chopped semisweet chocolate, 1 tablespoon butter and a pinch of salt; whisk until smooth. Spread over the cooled bars. Chill until set. 

39. Everything Bars Mix 2 cups each crushed plain potato chips and salted peanuts with 1 cup each shredded sweetened coconut, chocolate chips, raisins and toffee bits. Gently press into the prepared pan; top with one 14-ounce can sweetened condensed milk. Bake until bubbling around the edges, about 30 minutes. Let cool, then chill until set. 

40. Tropical Bars Mix 2 cups finely ground graham crackers with 1 stick melted butter. Press into the prepared pan and top with 1 1/2 cups each chopped salted macadamia nuts and unsweetened coconut flakes and 1 cup each chopped dried pineapple and white chocolate chips. Top with one 14-ounce can sweetened condensed milk mixed with 1/2 cup cream of coconut. Bake until bubbling around the edges, 30 to 35 minutes.

41. Honey Granola Bars Toast 3 cups rolled oats, 1 cup sliced almonds and 1/2 cup salted sunflower seeds on a rimmed baking sheet at 350 degrees F, 10 minutes. Melt 6 tablespoons butter with 1/3 cup brown sugar, 1/2 cup honey, 2 teaspoons vanilla and 1 teaspoon salt until the sugar is dissolved. Stir in the oat mixture and 1 cup chopped assorted dried fruit. Bake until lightly browned, about 20 minutes. 

42. Triple-Berry Granola Bars Make Honey Granola Bars (No. 41), omitting the almonds and using 2/3 cup each dried blueberries, dried cranberries and chopped dried strawberries for the assorted fruit. 

43. Trail Mix Granola Bars Make Honey Granola Bars (No. 41), replacing the almonds with salted peanuts and the dried fruit with 1/2 cup each raisins and mini M&M's. 

44. No-Bake Date-Nut Bars Soak 5 cups pitted dates in hot water, 10 minutes; drain. Toss with 2 cups each salted cashews and almonds, 1 cup each golden raisins and unsweetened shredded coconut, and 2 teaspoons grated lemon zest. Working in batches, pulse in a food processor until coarsely ground. Press into the prepared pan; press 1/4 cup more coconut into the top. Chill until set.

45. No-Bake Apricot-Pistachio Bars Make No-Bake Date-Nut Bars (No. 44), replacing the cashews with pistachios and the coconut with chopped dried apricots. Add 1/2 teaspoon each ground cardamom and grated orange zest to the food processor; omit the coconut topping. 

46. No-Bake Cereal Bars Melt 6 tablespoons butter with one 10-ounce bag mini marshmallows in a large pot, stirring, until smooth. Gently stir in 1/2 cup almond butter, 1 tablespoon honey, 1 teaspoon vanilla and 1/2 teaspoon salt. Stir in 8 cups assorted cereal and 1 cup salted almonds. Press into the prepared pan and let cool. 

47. No-Bake Salted Caramel Cereal Bars Make No-Bake Cereal Bars (No. 46), replacing the almond butter and honey with 1/2 cup jarred dulce de leche; use 3/4 teaspoon salt. Use 9 cups assorted cereal and omit the almonds. Sprinkle with flaky sea salt.

48. No-Bake Fruity Cereal Bars Make No-Bake Cereal Bars (No. 46), omitting the almond butter. Replace the assorted cereal with crispy rice cereal and the almonds with 3/4 cup each crushed freeze-dried raspberries and freeze-dried bananas. 

49. No-Bake Chocolate–Peanut Butter Cereal Bars Melt 1/2 stick butter with one 10-ounce bag mini marshmallows and 1/2 cup creamy peanut butter in a large pot, stirring, until smooth. Stir in 8 cups chocolate crispy rice cereal, then 1/2 cup mini chocolate chips. Press into the prepared pan and let cool. 

50. No-Bake S'mores Cookie Dough Bars Beat 1 stick softened butter with 1 cup light brown sugar and 1 teaspoon vanilla with a mixer on medium-high speed until fluffy. Reduce the speed to low. Add 2 cups finely ground graham crackers and 1 cup flour; beat until combined. Beat in one 14-ounce can sweetened condensed milk. Stir in 1 cup each milk chocolate chips and mini marshmallows. Press into the prepared pan and chill until set.

Photographs by Justin Walker