How to make muffins:
Line the pan(s) with paper or foil liners; coat the liners with cooking spray. (For savory muffins, dust with flour after spraying.)
Fill each liner 2/3 to 3/4 full with batter and bake at 350 degrees F until a toothpick comes out clean.
1. Streusel Make the topping: Mix 2/3 cup each chopped pecans, brown sugar and flour, and 1/4 teaspoon salt; work in 5 tablespoons cold cubed butter. Make the batter: Mix 2 cups flour, 1 teaspoon baking powder, 1/2 teaspoon each cinnamon and salt, and 1/4 teaspoon baking soda. Whisk 3 eggs, 3/4 cup sugar, 1 stick melted butter, 1 cup sour cream and 1 teaspoon vanilla; fold into the flour mixture. Divide among 12 prepared muffin cups, sprinkle with the topping and bake 20 to 25 minutes.
2. Earl Grey Make Streusel Muffins (No. 1), replacing the pecans with oats, reducing the sour cream to 3/4 cup and adding 1/3 cup strong Earl Grey tea with the vanilla.
3. Coffee Cake Make Streusel Muffins (No. 1), doubling the topping; divide among 18 prepared muffin cups and bake.
4. Snickerdoodle Make cinnamon crumble: Mix 2/3 cup sugar, 1/3 cup flour and 1 tablespoon cinnamon; mash in 1/2 stick softened butter. Make the batter for Streusel Muffins (No. 1). Stir 1/2 cup of the cinnamon crumble into the batter; divide among 12 prepared muffin cups and top with the remaining crumble. Bake 25 to 28 minutes.
5. Ginger-Lemon Minis Make Gingerbread Muffins (No. 6), dividing the batter among 36 to 48 prepared mini muffin cups. Bake 16 to 18 minutes. Make a dent in each muffin while still warm; cool. Fill with jarred lemon curd.
6. Gingerbread Mix 2 cups flour, 2 tablespoons cocoa powder, 1 tablespoon ground ginger, 1 teaspoon baking soda and 1/2 teaspoon salt. Whisk 1 stick melted butter, 1/2 cup each sugar and molasses, 1/4 cup milk and 2 eggs; fold into the flour mixture. Divide among 12 prepared muffin cups; bake 20 to 25 minutes.
7. Ginger-Fig Make Gingerbread Muffins (No. 6), adding 1/4 cup finely chopped dried figs and 1/4 teaspoon orange zest with the eggs.
8. Sugar-and-Spice Minis Make Gingerbread Muffins (No. 6), adding 1/2 teaspoon pepper with the flour and 1 tablespoon finely grated ginger with the eggs. Divide among 36 to 48 prepared mini muffin cups and sprinkle with chopped crystallized ginger. Bake 16 to 18 minutes.
9. Banana Mix 2 cups flour, 1/2 cup chopped nuts, 1 teaspoon baking powder, 1/2
teaspoon salt and 1/4 teaspoon baking soda. Whisk 3/4 cup brown sugar, 1 stick melted butter, 1/2 cup each mashed banana and sour cream, and 2 eggs; fold into the flour mixture. Divide among 12 prepared muffin cups; bake 20 to 25 minutes.
10. Apple-Cranberry Make Banana Muffins (No. 9), adding 1/2 teaspoon cinnamon with the flour and replacing the nuts with dried cranberries and the banana with applesauce. Top with dried apples and dried cranberries before baking.