Preheat oven to 350 degrees F. Liberally grease two 9" springform pans with cooking spray and place a parchment round in the bottom of each pan. Spray the parchment lightly with cooking spray; set aside.

In two large bowls, prepare the brownie batter according to package directions. Pour the brownie batters into the prepared pans. Bake for approximately 30-35 minutes or until a toothpick inserted near the center comes out clean or with moist, not wet, crumbs. Cool completely, then gently release from the pans. Place one brownie layer upside down on a cake platter.

To make the cookie dough filling: In the bowl of a stand mixer, cream together butter, brown sugar, and granulated sugar together on medium speed for about 1 minute or until creamy. Beat in the vanilla and heavy whipping cream/milk, followed by the flour or flour substitute, until a soft dough has formed. Stir in the miniature chocolate chips and Oreo cookie pieces.

Spread the cookie dough on top of the brownie layer in an even layer. Filling layer will be thick. Top with the remaining brownie layer and press down gently to adhere.

For the ganache, microwave the heavy whipping cream for 30-35 seconds or until hot. Pour over the semi-sweet chocolate chips in a medium bowl and microwave that mixture for 10-20 seconds. Leave in the microwave for about 1 minute to allow chocolate chips to melt. Stir the mixture until smooth and glossy, then pour the ganache evenly over the top of the top brownie layer and down the sides of the cake.

Immediately put handfuls of chopped brownies, chocolate chip cookies and Oreo cookies all over the ganache's surface. Serve immediately, or keep in the fridge up to 2 days.