1. Prepare a 9-inch springform pan by lining the sides with parchment paper that sticks about an inch above the sides of the pan.
2. To make the mocha mousse, bring the milk to a boil in a small measuring glass, then dissolve powdered espresso in the milk. Allow to cool.
3. Put the chocolate chips for the ganache in a heat proof bowl. Heat heavy whipping cream for ganache until it comes to a boil, then pour over the chocolate chips. Allow to sit covered for about 5 minutes, then whisk until smooth. Set aside to cool a bit and thicken.
4. Beat cream cheese and sugar for mocha mousse together in a large mixer bowl until smooth.
5. Slowly add espresso mixture to cream cheese mixture and beat until smooth. Set cream cheese mixture aside and make whipped cream.
6. Whip heavy whipping cream on high until it begins to thicken. Add vanilla extract and powdered sugar and continue to whip on high until stiff peaks form.
7. Carefully fold whipped cream into espresso cream cheese mixture.
8. Place a single layer of wafer cookies on the bottom of the pan, then top with about 1/3 of the espresso mixture (about 2 1/3 cups). Spread about 1/3 of the ganache (about 1/2 cup) evenly on top of the espresso mixture.
9. Repeat previous step two more times so that you have 3 of each layer. Refrigerate until firm, 4-5 hours
10. Once firm, remove icebox cake from pan.
11. To make whipped cream for topping, whip heavy whipping cream on high until it begins to thicken. Add vanilla extract and powdered sugar and continue to whip on high until stiff peaks form.
12. Pipe the whipped cream around the top edge of the cake, then drizzle with chocolate sauce. Finish off cake with chocolate covered espresso beans, if desired.
13. Refrigerate until ready to serve.