an 18-by-13-inch sheet pan; a pastry bag; a kitchen torch, optional
Preheat the oven to 325 degrees F. Spray an 18-by-13-inch sheet pan with cooking spray and top with parchment, leaving a 1-inch overhang on each of the short sides. Spray the parchment with cooking spray.
Remove 1/4 cup of the cookie dough and reserve. Divide the remaining cookie dough into 3 equal portions. With the long sides of the prepared sheet pan positioned horizontally in front of you, visualize the pan divided into 8 even sections: 4 sections in the top row and 4 sections in the bottom row. Press one portion of the cookie dough into the top right section. Press a second portion of the dough into the section diagonally below and to the left of the first. Press the last portion of the dough into the bottom left corner.
Prepare the brownie batter according to the package directions. Divide the batter among the remaining 5 sections (about 1/2 cup batter per section).
Working from left to right on the top row, swirl 1 tablespoon of the peanut butter into the brownie batter in the top left corner. Press 6 of the chocolate sandwich cookies on top of the batter in the next section. Roll the reserved cookie dough into balls and arrange on top of each chocolate sandwich cookie and in the large diamond-shaped gaps between the cookies (do not place the balls too close to the edges of the section, or they may spread into the other sections). Swirl the dulce de leche into the batter in the next section and top with a sprinkle of coarse sea salt. Press the candy-coated chocolates into the cookie dough in the top right section.
Working from left to right on the bottom row, press the crushed potato chips into the cookie dough in the first section, then arrange the pretzels on top. Press the graham cracker bears into the brownie batter in the next section. Top the next cookie section with alternating rows of cream cheese bits and white chocolate chips. Last, sprinkle the semisweet chocolate chips on the final section of brownie batter.
Bake until the cookies are golden and the brownies are set, 25 to 30 minutes. Cool for 10 minutes in the pan on a rack.
Meanwhile, prepare the toppings: Microwave the remaining 1 tablespoon peanut butter in a small microwave-safe bowl until smooth and pourable, about 15 seconds. Crush the remaining 2 chocolate sandwich cookies. Transfer the frosting to a pastry bag.
Drizzle the warm peanut butter over the swirled peanut-butter brownie section and top with the crushed peanuts. Sprinkle the remaining crushed chocolate sandwich cookies over the section containing the whole cookies. Swirl the frosting over the candy-coated chocolate candy section and top with the rainbow sprinkles. Top the graham cracker bears with the mini marshmallows and toast with a small kitchen torch (or broil the marshmallows under a low broiler for about 1 minute). Last, sprinkle the freeze-dried raspberries over the chocolate chip brownie on the bottom right.
Lift the finished brownie-cookie bar out of the pan and remove the parchment paper. Slice vertically in 8 pieces and horizontally in 4 pieces to create multi-flavored pieces.
Propane gas torches are highly flammable and should be kept away from heat, open flame and prolonged exposure to sunlight. They should be used only in well-ventilated areas. Follow torch manufacturer's instructions for use.
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