Preheat oven to 350 degrees. Line 3, 8" pans with parchment paper. Flour & butter sides of pans.

Whisk together first six ingredients in mixing bowl. Then add following 7 ingredients and beat on medium speed until all ingredients well combined, about 2 minutes. The batter is thin.

Divide batter evenly among the three prepared pans. Bake until toothpick comes out of center of cake with just a few crumbs, about 25 minutes. Let cool for at least 5 minutes before removing from pans. Let cool completely before frosting.

In large bowl or stand mixer with whisk attachment, beat eggs for about 4 minutes, or until light colored and thickened. Then, beat in sugar.

Heat ½ cup of heavy cream in a medium sized sauce pot over medium heat until it begins to bubble. Then, slowly pour a little over half of the cream into the egg yolk mixture, stirring continuously. Pour the mixture back into the remaining heavy cream in the pot, still stirring continuously. Turn heat under pot to low, and stir continuously until mixture begins to thicken, about 5 minutes. After mixture has thickened, remove from heat and whisk in chocolate chips until smooth.

Place the egg mixture in a bowl in the refrigerator for at least two hours. After mixture has chilled, beat remaining 1/2 cup of whipping cream with whisk attachment until stiff peaks form, about 5 minutes. Fold whipped cream into chocolate/egg mixture until well combined.

Use electric mixer to beat together butter and shortening until light and fluffy, about 3 minutes.

In a small bowl, stir together salt, cocoa powder, and powdered sugar. Beat into butter mixture, about ½ cup at a time. Then mix in vanilla and whipping cream. Beat for an additional 1-2 minutes, or until smooth and fluffy.

Level cooled cake layers. Pipe buttercream around outside edge of two layers. Divide mousse between the two layers. Stack filled layers on top of each other and place third layer leveled side down on top.

Apply a thin layer of buttercream to outside of entire cake. Place cake in refrigerator for 10-20 minutes. After this, finish frosting and decorating as desired. Grate Hershey’s bar to sprinkle over top of cake and/or press into sides of cake.