Preheat oven to 350-degrees.
Whisk together dry ingredients with the exception of the espresso powder.
In a separate bowl, beat the buttermilk, eggs, vanilla and oil.
Mix boiling water and espresso powder.
Add mixture to batter and mix well.
Divide batter and pour evenly into two 6-1/2" x 3" greased and floured baking pans.
Bake for 40 minutes until toothpick test has a dry result.
Cool pans on a baking tray.
Pour cakes out of pans, level the tops with a serrated blade, cut cakes in half to create 4 layers.
Add frosting between layers before frosting entire cake.
Dust the top of the cake with a small amount of cocoa powder (optional).
Whisk lumps out of the powdered cocoa.
Add butter and mix in stand mixer until creamy.
Add the confectioner's sugar, one cup at a time, alternating with milk. Mix well between each alternate add.
Add vanilla and espresso powder.
Mix in stand mixer until super creamy.