• Preheat the oven to 350°F. Spray a 9×13-inch baking dish with non-stick spray.

Crust

• Using a food processor, process Oreos cookies until they are a fine crumb. Set aside ¼ cup crumbs for the topping.
• In a large bowl, combine the remaining cookie crumbs with melted butter until fully incorporated.
• Press cookie mixture into the baking dish. Set aside.

Brownie Layer

• To a large bowl add flour, cocoa, baking powder, and salt. Whisk together ingredients until they are fully incorporated.
• In the bowl of a stand mixer or in a large bowl using a hand-held mixer beat the eggs, sugar, butter, and vanilla until light and fluffy.
• With the mixer off, add the flour mixture. Turn the mixer on low and mix until the ingredients are well combined.
• Carefully pour brownie batter into the prepared baking dish, over the Oreo cookie crust. Bake for 25-30 minutes, or until just barely set. (Keep a close eye on it, looking for a fudgy layer). A toothpick inserted in the center will have a small amount of wet batter. Set aside to cool to room temperature.

Chocolate Mousse Layer

• In another large bowl, beat the milk, pudding mix, and confectioners' sugar until soft-set (about 2 minutes).
• Fold in 8 ounces of whipped topping and continue folding until fully combined. Spread over the cooled brownie layer. (Don't put the mousse on hot brownies; make sure the layer is mostly cooled.)
• Transfer the bars to the refrigerator to chill for at least 1-1 ½ hours.
• Once chilled, drizzle hot fudge over the mousse. Top with the remaining whipped cream and reserved cookie crumbs. Enjoy immediately or store in the refrigerator until ready to serve.