Peeps S'mores Brownies

Preheat oven to 325 degrees F. Line a 8 x 8" baking pan with aluminum foil or parchment paper, leaving overhang on the sides. Spray with nonstick cooking spray and set aside. Make the crust: In a bowl, combine melted butter and graham cracker crumbs. Press into prepared pan and set aside. Make the brownies: In a large microwave-safe bowl, combine butter, sugar, cocoa powder, and salt and heat on high to melt, about 45 seconds. Stir, then heat in 10-second bursts until mixture has melted and can be stirred until smooth. (Batter will be very granular.) Add vanilla and eggs and stir vigorously until batter is thick, shiny, and well blended. Add flour and stir until you cannot see it any longer. Fold in chocolate chips. Pour half the batter into prepared pan and spread evenly. Dollop half the marshmallow fluff all over the batter and swirl slightly with a knife. Spread remaining batter carefully over marshmallow fluff. Repeat with remaining marshmallow on top of brownie batter. With a knife, carefully swirl marshmallow fluff into batter. Bake until a toothpick in the center emerges slightly moist with batter, about 25 minutes. Top with Peeps and bake until Peeps are puffed up and melted together, 3 to 5 minutes more. Cool brownies completely before cutting into 16 equal squares with a very sharp knife. Brownies will keep in an airtight container at room temperature or in the refrigerator for up to 1 week.