This decadent, no-bake chocolate peanut butter mousse cake is made with layers of crunchy, buttery chocolate cookie crust, fluffy peanut butter mousse and rich chocolate mousse. It's topped with satiny smooth chocolate ganache glaze and tastes absolutely incredible!
Lightly grease the bottom and sides of a 9-inch springform pan that's at least 3-inches high.
Make the crust: Combine cookie crumbs and melted butter in a medium-sized bowl and mix until combined and moistened. Press the mixture firmly into the bottom of the pan. Place in the fridge to chill while you make the peanut butter mousse. (Note: While it's not required, you can bake the crust for 7-8 minutes in a preheated 350°F/180°C oven. This helps the crust solidify and makes it crunchier. After baking, allow it cool completely on a wire rack before adding the peanut butter mousse filling).
Make the peanut butter mousse: In an electric mixer bowl fitted with a paddle attachment, beat cream cheese on medium-high speed until fluffy. Add the softened butter and combine until creamy, about 1 minute. Add powdered sugar and beat until combined and fluffy. Beat in peanut butter, salt, and vanilla extract. Set aside.*
In an electric mixer fitted with the whisk attachment or using a handheld mixer, whisk heavy cream until soft peaks form; they should hold their shape but have a soft texture. Using a spatula, gently fold 1 cup of the whipped cream into the peanut butter mixture, then fold in another 1 ½ cups (Note: there will be leftover whipped cream for the chocolate mousse. Cover and place in the fridge to keep cold until ready to use).
Scrape the peanut butter mousse on top of the crust and smooth into an even layer. Refrigerate while you make the chocolate mousse.
Make the chocolate mousse: Place the bittersweet and milk chocolates along with the milk in a microwave-safe bowl. Microwave in 30-second increments, stirring between each interval until melted. Alternatively, you can do this on the stove in a double boiler. Stir in the vanilla extract and allow to cool for 5 minutes.
Gently fold in half of the remaining cream with a rubber spatula, then fold in the other half. Pour on top of the peanut butter mousse layer and smooth into an even layer. Cover loosely and place the cake in the freezer or fridge for one hour.
Make the chocolate ganache glaze: Place chocolate and cream in a microwave-safe bowl and heat in 30-second increments, stirring in between each until fully melted. Pour the glaze on top of the cake, using a knife to spread evenly. place
Cover pan loosely with plastic wrap and place in the fridge for at least 6 hours, or until completely set, before serving.
Release the cake from the pan: Run a knife under hot water and dry it. Then, slide the heated knife between the cake and the inside of the pan to release it. Slowly remove the sides of the pan. Serve the cake cold.
Chocolate mousse cake will keep for 5 days in the fridge.
*If the mousse appears clumpy, you can either strain it using a fine mesh strainer or blend it together using an immersion blender or standing blender. The lumps are most likely because the cream cheese wasn't soft enough - but not to worry, this is easily fixable!