Add the granulated sugar, cocoa powder, cornstarch, and salt to a medium-sized non-stick pot and whisk to combine. Whist in the egg yolk and milk.

Heat over medium heat, whisking constantly until the mixture comes to a boil and has thickened.

Remove from the heat and whisk in the butter, espresso powder, vanilla extract, and the chopped chocolate. Whisk until the butter and chocolate have melted and the pudding is smooth.

Place a fine-mesh strainer over a glass bowl and pour the pudding over the strainer. Whisk the pudding until it all passes through the strainer and any lumps are left behind.

Place a piece of plastic wrap directly on the pudding surface and cool to room temperature. Then refrigerate the pudding for at least 2 hours or overnight.

Preheat oven to 350 degrees. Spray 2 8-inch round cake pans with non-stick spray and line the bottom of the pans with parchment circles.

In a large bowl, whisk together the eggs, water, oil, and espresso powder until combined. Stir in the chocolate cake mix until completely incorporated.

Divide the batter evenly between the 2 cake pans. Bake for 25-35 minutes or until a cake tester comes out clean. When done, the cake will spring back when pressed and will pull away from the sides of the pan.

Cool the cakes in the pan for 10 minutes then remove from the pans and cool completely on a wire rack.

Make the Chocolate Cream Cheese Frosting or Chocolate Buttercream Frosting as directed.

Use a serrated knife to slice the domed top off the cakes to level them. Set the cake tops/pieces aside to use for garnish.

Place one layer of the cake on a cake stand or cake plate. Spread a very thin layer of frosting over the cake, just enough to cover and form a barrier for the pudding.

Add some of the frosting to a piping bag fitted with a large round tip. Pipe a dam/frosting ring around the edge of the cake. Refrigerate or freeze this layer for 10-15 minutes to solidify the frosting.

Once the frosting ring/dam has firmed up, continue assembling the cake. Spoon the chocolate pudding inside the frosting dam and spread evenly to the edges.

Place the second layer of cake on top. Frost the top and sides of the cake with the remaining frosting.

Crumble the reserved cake pieces and press into the sides and top of the cake to garnish.

Refrigerate the cake until ready to serve. Bring the cake to room temperature 30 minutes to 1 hour before serving.