For the Cake:

Preheat the oven to 350 degrees F.  Grease and lightly flour 2 8 or 9 inch round cake pans.  Prepare the cake mix based on the package instructions and bake the cake in the round cake pans.

Let the cake cool in the pans for approximately 10 minutes, then gently remove the cakes from the cake pans and allow the cakes to cool completely on wire racks.  Then refrigerate the cakes so that they are easier to handle.

For the Mouse:

Whisk together the cocoa powder and the hot water.  Place the chocolate chips in a separate microwave safe bowl.  Microwave in 30 second intervals, stirring after each interval, until the chocolate chips are just melted.  Stir the cocoa mixture into the melted chocolate chips.

In a separate chilled bowl, beat the heavy whipping cream with the powdered sugar with a stand up mixer or hand held mixer until stiff peaks form.  Gently fold the chocolate mixture into the whipped cream until well combined.  Refrigerate until you are ready to assemble the cake.

For the Frosting:

In a separate chilled mixing bowl, beat together the frosting ingredients with a stand up mixer or hand held mixer until soft peaks are formed.  Refrigerate until you are ready to assemble the cake.

To Assemble the Cake:

Cut each cake in half horizontally to make 4 cakes and trim off the rounded tops to make them level.

Place one of the cakes (cut side up) on a serving plate, spread 1/3 of the chocolate mousse mixture on top.  Then repeat this process 2 more times until all the mousse is used.  Then top the cake with the fourth cake (cut side down).

Spread the frosting on top of the cake and over the sides of the cake.  Cover the cake and refrigerate for at least 1 hour before serving.

Then the cake is ready to slice, serve and enjoy!