• Turn oven to 300°F to preheat.
• Mix the flour, sugar, cocoa powder, baking soda, and salt together in a large mixing bowl.
• Whisk in the eggs, buttermilk, oil, and vanilla. Then add in the hot coffee (or water).
• Prepare three 8 inch cake pans with baking spray (or grease and dust with flour) and divide the batter evenly among them.
• Bake in the preheated oven for 30-35 minutes. The cake is ready when the center doesn't jiggle at all and feels slightly springy when you touch it.
• Allow the cakes to cool in the pans for 10 minutes, then flip them onto cooling racks to finish cooling completely.

For the Frosting

• Beat the butter and shortening together until well mixed.
• Slowly beat in 4 1/4 cups of the powdered sugar.
• Then beat in the vanilla and 2 tablespoons of the milk.
• Slowly beat in the remaining 4 cups of powdered sugar.
• Beat in 2-3 more tablespoons of milk. (You may keep adding milk-- a couple tablespoons at a time-- until the frosting is thinner, if you prefer)

Assemble the Cake

• Place the first cake layer on a platter and spread a thin layer of frosting on its top. Using a piping bag with a couple, but no tip, pipe a barrier around the edge of the cake.
• Sprinkle half of the toasted hazelnuts on top of the cake, inside the frosting barrier.
• Place another cake layer on top of that and repeat with more frosting and the remaining hazelnuts.
• Place the last layer on top and frost the whole cake with the remaining frosting.