Preheat your oven to 350°F (175°C) and prepare two round cake pans by greasing them and lining the bottoms with parchment paper. In a microwave-safe bowl, melt unsalted butter. Stir in granulated sugar and brown sugar until glossy, then mix in eggs, vanilla extract, cocoa powder, flour, and salt. Divide the batter between the pans and bake for 30 minutes. Let them cool completely in the pans on a wire rack.

Increase the oven temperature to 425°F (220°C) for the cheesecake layers. In a large mixing bowl, beat full-fat cream cheese until light and fluffy, then gradually add granulated sugar. Add in eggs one at a time, mixing well after each addition, followed by sour cream and vanilla extract. Pour the cheesecake batter into the greased pans and bake for 25 minutes or until the edges are set but the center is slightly jiggly. Allow layers to cool before placing them in the freezer to chill.

While the cheesecake layers chill, prepare the chocolate chip cookie layers by preheating your oven to 350°F (175°C). Line two more cake pans with parchment and gently spread the chocolate chip cookie dough evenly across the bottom. Bake for about 12 minutes, or until the edges are golden. Remove them from the oven and let them cool in the pans on a wire rack.

In a separate bowl, prepare the chocolate frosting by mixing cocoa powder, softened unsalted butter, powdered sugar, and milk until creamy and smooth. For the marshmallow frosting, combine marshmallow fluff and softened butter in a bowl, then gradually add powdered sugar and vanilla extract while beating until light and fluffy. Set both frostings aside for assembly.

To create your 7 Layer Sin Cake, start with a brownie layer as the base. Spread a generous layer of marshmallow frosting on top, followed by a chocolate chip cookie layer. Repeat the process with another marshmallow frosting layer, then add a cheesecake layer. Next, spread chocolate frosting on top and place crushed graham crackers evenly. Continue layering in the same order until all elements are used, topping the final layer with chocolate frosting.

Once your cake is fully assembled, smooth the remaining chocolate frosting around the sides and on top of the cake. Decorate with extra graham cracker crumbs or chocolate chip cookies as desired. Allow the 7 Layer Sin Cake to set in the refrigerator for at least an hour before slicing.