Make the Cake

Cup of Yum
1. Preheat your oven to 350 degrees F.
2. Put your cake mix in a large bowl and add the eggs your cake mix calls for, plus one extra.
3. Substitute the oil called for on the boxed mix for the same amount of melted butter.
4. Replace the water called for on the boxed mix with the same amount of milk.
5. Whisk your cake mix until combined.
6. Grease two 9-inch cake pans and divide the batter evenly between the 2 pans.
7. Bake for 20 minutes or until a toothpick inserted in the middle comes out clean.
8. Cool the cakes completely.

Make the Mousse and Assemble

1. Chocolate cakes often have a domed top due to the natural rising process during baking. Once the layers are cool, it's necessary to level the cake by slicing off the rounded tops. Set the cake you sliced off aside for later use.
2. In a large bowl, combine the heavy whipping cream with the dry instant pudding mix. Beat with an electric mixer until combined and fluffy.
3. Place down one cooled cake layer on a cake platter.
4. Add all the mousse.
5. Top with the remaining cake layer.

Make the Frosting

1. In a microwave-safe bowl in 30-second intervals, melt your chocolate chips with the corn syrup.
2. Set aside to cool but not harden.
3. Next, whip together the butter, powdered sugar, cocoa, and vanilla in a large bowl using an electric mixer.
4. Beat in the cooled chocolate mixture.
5. Frost the cake with a knife or offset spatula. Use a piping bag or plastic bag with the tip cut-off pipe around the edges. Use a fork to make squiggly lines across the top.
6. At Costco, the outside of this cake has a chocolate crumb coating. It is totally optional, but if you want the look, crumble the cake tops you cut off the cake in step #4 very finely and press the crumbs into the side of the cake.