Make the Mousse Layers

1. Prepare a 9-inch springform pan by lining the sides with parchment paper or an acetate collar that sticks about an inch above the sides of the pan.
2. In a larger mixer bowl, beat the cream cheese and sugar together until smooth.
3. Add the milk and beat until smooth. Set cream cheese mixture aside.
4. Make whipped cream by whipping the cream on high with a mixer until it begins to thicken. Add vanilla extract and powdered sugar and continue to whip on high until stiff peaks form.
5. Carefully fold 1/3 of the whipped cream into the cream cheese mixture until combined. Add the remaining whipped cream and fold mixtures together until well combined.
6. Divide the mousse into two bowls. You’ll want twice the amount in one bowl as the other. You should have about 2 1/3 cups in one bowl and the rest in another.
7. Add the peanut butter to the bowl with the larger amount of mousse and fold to combine. Set aside.
8. Add the cocoa to the smaller amount and fold to combine. Set aside.

Assemble the Cake Layers

1. Pour the milk into a small bowl. Begin dipping cookies in the milk and placing them in a single layer on the bottom of the pan.
2. Top the dipped cookie layer with half of the peanut butter mousse and spread into an even layer.
3. Add another layer of milk-dipped cookies on top of the peanut butter mixture.
4. Top this cookie layer with the chocolate mousse and spread into an even layer.
5. Continue dipping cookies in milk and layer them on top of the chocolate mixture in a single layer.
6. Top the cookies with the remaining peanut butter mousse and spread into an even layer.
7. Refrigerate cake until firm, 4-5 hours or overnight.

Finish the Cake

1. Once firm, remove icebox cake from pan.
2. Make chocolate whipped cream topping by whipping heavy cream on high until it begins to thicken. Add the powdered sugar and cocoa powder and continue to whip on high until stiff peaks form.
3. Pipe the whipped cream around the top edge of the cake, then drizzle with chocolate sauce. Finish off cake with chopped Mini Reese’s, if desired.
4. Refrigerate until ready to serve. Best if eaten within 3-4 days.