Chocolate Peanut Butter Mousse Cake

(Adapted from Tish Boyle's "The Cake Book")
(makes one 9-inch cake)

Chocolate Wafer Crust

1 1/2 cups (6.3oz) Nabisco Famous Chocolate Wafer cookie crumbs
4 tbsp (2oz) unsalted butter, melted

Peanut Butter Mousse

5 ounces cream cheese, softened
2 tbsp (1oz) unsalted butter, softened
1 cup (4oz) confectioners' sugar
3/4 cup (7oz) creamy peanut butter
1/4 tsp salt
2 1/2 cups heavy whipping cream

Chocolate Mousse

5 ounces bittersweet chocolate, coarsely chopped
3 ounces milk chocolate, coarsely chopped
1/3 cup whole milk
3 tbsp granulated sugar
1/2 tsp vanilla extract

To make the crust:

Lightly butter the bottom of a 9x3 inch springform pan. In a bowl, stir together the cookie crumbs and the melted butter until combined. Press the crumbs onto the bottom of the pan in an even layer. Refrigerate the crust while you make the PB mousse.

To make the PB mousse:

In the bowl of a standing mixer using the paddle attachment, beat the cream cheese and butter until creamy, about 1 minute on medium-low speed. Mix in the confectioners' sugar. Add the peanut butter and salt and mix until well blended. Remove the bowl from the mixer and set aside.

In a clean mixer bowl, using the whisk attachment, beat the heavy whipping cream at high speed until soft peaks form. Fold 1 cup of the whipped cream into the peanut butter mixture until almost blended. Fold in another 1 1/2 cups of the whipped cream until completed blended. (Save the remaining whipped cream for making the chocolate mousse.)

Scrape the peanut butter mousse into the prepared pan and spread evenly over the crust. Refrigerate while you make the chocolate mousse.

To make the chocolate mousse:
Place both chocolates in the bowl of a food processor and process until finely ground. Leave the chocolate in the bowl.

Combine the milk and sugar in a small saucepan and bring to a boil over medium heat. With the food processor running, pour the hot milk mixture through the feed tube and process until the chocolate is completely melted. Scrape down the sides of the bowl, add the vanilla, and process until blended. Scrape mixture into a large bowl.

Gently fold one-third of the remaining whipped cream into the chocolate. Fold in the rest of the whipped cream until completely blended. Scrape the chocolate mousse over the peanut butter mousse layer. Loosely cover the cake and freeze for at least 1 hour, until firm.

To serve:
Run a thin-bladed knife under hot water (or dunk into a pitcher of hot water) and wipe dry, run the knife between the cake and the side of the pan to release the cake; reheat the knife as needed. Remove the sides of the springform pan. The cake is ready for serving. Store in refrigerator for up to 3 days.