Bake according to directions on box using 2 round pans, then cool. Once cooled, use the cake from one pan as one layer (you do not need the second cake from the second pan. In other words, you only need half the box cake recipe). Place this round cake at the bottom of a CHEESECAKE PAN. Press it with your fingers and flatten the cake a little. This is the bottom layer out of four layers.
SECOND LAYER (the chocolate mousse):
Melt chocolate and cream cheese together. Let cool. Soften gelatin with cold water for 1 minute, then add boiling water, stir until dissolved and clear. Let this cool while you start whipping the heavy cream and sugar. As cream starts to thicken, add gelatin. Continue to whip until stiff peaks form. Add 1/4 of the cream to the chocolate mixture and mix thoroughly. Then fold this into the remaining cream. Once you have it completed, spread this chocolate mousse onto the cake and refrigerate.
THIRD LAYER (the custard):
Beat egg yolks until pale. Add sugar, flour, and gelatin, then beat until mixed. Bring cream and vanilla extract to a boil. Add a small amount of cream to egg mixture while stirring. Gradually add until all of the cream has been added and then pour entire mixture through a strainer into the pan. Continue to cook until custard begins to thicken. Cool slightly, then pour on top of the chocolate mousse layer and freeze while getting the fourth layer ready.
FOURTH LAYER (the icing):
Please note: this makes a lot of icing so feel free to half this part of the recipe (I just happen to like a lot of icing on top). Bring butter and cream to a boil, pour over chocolate and let sit for 5 minutes. Stir until smooth. Let cool until it starts to thicken. Remove cake from freezer, remove the cheesecake pan collar, then pour some of the icing and use a spatula to spread it evenly across the top and sides of the cake. While this is still wet, put chocolate chips onto the side of the cake. Optional: Melt half a cup of white chocolate chips (in the microwave) and swirl into the icing if you want yours to look like the picture.
Refrigerate the cake. Be sure to see the picture. Serve cold. Delicious!