• Preheat the oven to 350°F.
• Grease a pair of 8-inch round cake pans with cake goop (see notes), butter or shortening and dust with flour. Set aside.

Prepare the Cake Batter

• Whisk the flour, sugar, cocoa powder, baking powder, baking soda and salt together in a large mixing bowl.
• Use an electric mixer to mix in the oil until the mixture is clumpy.
• Add the eggs and vanilla extract and mix until combined.
• Pour in the buttermilk and coffee and mix at low speed to keep the mixture from splashing out of the bowl until the batter is well mixed. It will be thin like pancake batter.

Bake the Cake

• Divide the batter evenly between the prepared cake pans and bake on the middle rack of the oven for 30 minutes or until a toothpick inserted in the middle of the cakes comes out clean.
• Let the cakes cool in the pans for 30 minutes before transferring them to a wire rack to cool completely.

Prepare the Ermine Frosting Filling

• Whisk the sugar, salt and flour in a small saucepan over medium heat for 1 minute.
• Pour in the milk and whisk until smooth. Keep whisking to prevent the mixture from scorching on the bottom.
• Once the mixture thickens significantly (like paste or pudding) and starts to bubble, remove from heat, and pour it into a shallow, heat-proof container.
• Cover it with plastic wrap pressed on top to prevent a skin from forming and let it cool to room temperature on a cooling rack.
• Once cool, beat the butter and vanilla into the cooled milk mixture until light and fluffy.

Make the Chocolate Ganache

• Combine the chocolate chips and heavy whipping cream in a small, microwave-safe bowl, and heat in the microwave in 30-second increments, stirring in between each until the ganache is smooth.
• Let the ganache cool to room temperature.

Assemble the Ding Dong Cake

• If the cake layers have a dome, cut off the tops to make them flatter.
• Line a large plate or platter with parchment paper.
• Place one of the cake layers on the parchment paper.
• Spoon the ermine frosting filling on top of the cake and smooth it out into a thick, even layer.
• Place the second cake layer on top of the frosting and gently press it down.
• Use an offset spatula or the straight edge of a spatula to smooth out the frosting around the edge of the cake.
• Chill the cake for 30 minutes in the refrigerator.
• Pour the chocolate ganache on top of the cake, allowing it to pour down the sides of the cake.
• Smooth it out evenly and chill the cake for at least another 30 minutes or until the ganache is set.

Serve and Enjoy

• Carefully transfer the cake to a cake stand or plate.
• Slice and serve chilled or at room temperature.