Preheat oven to 350 degrees F. Grease and flour 2 8-inch cake pans. Line bottom of pan with parchment paper by tracing pan with a pencil and cutting paper so it just fits the bottom of the cake pans.

Place the cocoa powder in a medium-sized bowl, set aside.

In a medium-sized sauce pan melt the butter. Once melted add milk and Nutella and bring to a boil. Once at a steady boil pour over the cocoa powder and stir, then place in the fridge while you prepare the rest of the ingredients.

In a large bowl toss together the flour, sugar, baking powder, baking soda, and salt. Once combined pour the chilled Nutella mixture in a steady stream and stir to combine. Add the eggs one at a time stirring until just combined.

Pour the batter into the prepared cake pans and bake for 15 to 20 minutes or until a toothpick inserted in the center comes out clean or with a baked few crumbs.

Place on a cooling rack to cool completely before frosting, while the cakes cool make the frosting.

In a large mixing bowl with a handheld mixer or in a stand mixer, beat the butter until smooth and creamy. Mix in the powdered sugar one cup at a time, then add the cocoa powder. Beat until combined.

Add heavy cream one tablespoon at a time. Adjust the powdered sugar and heavy cream as needed to reach desired consistency.

Place a dollop of the frosting to the middle of a cake stand or serving plate. Loosen the cake that will be your bottom layer (you can run a butter knife along the edge). Invert that cake onto the stand (or plate) by putting the stand on top of the cake pan, holding them together and then just flip them over.

Spread ½ to 1 cup of Nutella on top of the first layer then invert the second layer on top of the Nutella. Spread the same amount of Nutella on top of the second layer.

Spread the buttercream frosting on the whole cake and garnish with chocolate chips if desired.