Prepare pudding according to package directions (use 4 ½ cups milk). Soften gelatin in liquid and heat until clear, set aside.
When pudding is thickened, add chocolate chips and stir or whisk until smooth. Add gelatin mixture; stir.
Place bowl in another bowl filled with ice water and whisk or stir until cool and very thick but still liquid. (Or cool by covering surface of pudding with plastic wrap and place in refrigerator for 2-3 hours until thick).
Whip cream with sugar. Fold ½ cup whipped cream into pudding, then fold in remaining cream. Spray pan with vegetable pan spray. Pour mousse into pan; tap lightly to spread.
Cover top with plastic wrap and place in freezer for 4 hours or refrigerate overnight or until very firm.
To unmold, loosen top edges with small pointed spatula. Invert on serving dish. If necessary, cover with hot towel or use hand held hair dryer to release.
If mousse is frozen, let thaw in refrigerator one hour before serving.
Decorate in Order
Prepare Chocolate Mousse Recipe and mold in pan prepared with vegetable pan spray; unmold when firm.
Spatula ice scoop areas with whipped topping. Immediately sprinkle with Rainbow Nonpareils Sprinkles.
Preheat oven to 350 For temperature per recipe directions. Your cake will unmold easily, without sticking, when you prepare the pan properly. Grease the inside of pan using a pastry brush and solid vegetable shortening (do not use butter, margarine or liquid vegetable oil). Spread the shortening so that all indentations are covered. Sprinkle about 2 Tablespoons flour inside pan and shake so that flour covers all greased surfaces.
Turn pan upside down and tap lightly to remove excess flour. If any shiny spots remain, touch up with more shortening and flour to prevent cake from sticking. (You can use vegetable oil pan spray or vegetable oil pan spray with flour, in place of solid shortening and flour, or use Wilton Cake Release, for perfect, crumb-free cakes or Bake Easy Non-Stick Spray for easy release).
Make one 2-layer cake mix according to package or recipe directions. Pour the cake batter into pan, and if necessary, spread the batter around with a spatula to fill all areas of the pan evenly. Be careful not to touch sides or bottom of pan.
Bake cake on middle rack of 350 F oven for 30-40 minutes or until cake tests done according to recipe directions.
Remove cake from oven and cool on cake rack for 10 minutes. While the cake is still in the pan, carefully slice off the raised center portion of the cake. This allows the cake to sit more level and helps prevent cracking.
To remove cake from pan, place cooling rack against cake and turn both cake rack and pan over. Lift pan off carefully. Cool cake at least one hour. Brush loose crumbs off cake. To transfer cake to serving board, hold a cake board against cake and turn both cake and rack over. Lift off rack. Hold another board against bottom of cake and turn cake over.
Be sure to hold cake, rack and board close together while turning to prevent cake from cracking.
We recommend hand washing pan in hot, soapy water.