Preheat the oven to 350°F and prepare three 8 inch round cake pans. Spray the inside with cooking spray, then cut round pieces of parchment paper so that they fit in the bottom of each pan (do not skip the parchment paper lining!) Whisk flour, cocoa powder, sugar, salt, baking powder, baking soda together in a large bowl.
Add in the eggs, vanilla, oil, and milk. Pour in the hot coffee and mix until smooth.
Divide the batter evenly between the three cake pans and bake on the middle rack of the oven for 20-26 minutes or until a toothpick inserted in the middle of the cakes comes out clean.
Let the cakes cool in the pans for 20 minutes, then run a butter knife around the outside of the cake to loosen it from the pan and flip upside down onto a cooling rack to cool completely.
Make the buttercream. In the bowl of a standing mixer or handheld mixer, beat butter until smooth. If using shortening, mix with the butter until combined.
Add in the vanilla extract, espresso powder, then add the icing sugar, 1/4 cup at a time until desired consistency is reached. If the buttercream is too thick, add in milk or brewed coffee 1 tablespoon at a time to thin it out to the consistency you want. If it's too thin, add in more confectioner's sugar (powdered sugar) 1/4 cup at a time.
Once the cakes have cooled completely, assemble and enjoy!