0 Preheat the oven to 350°F. Prepare your cake pans by rubbing butter all over the sides and bottom. Then, cut two circular pieces of parchment paper to place in the very bottom of the cake pans.
1 In a large bowl, whisk together the flour, sugar, cocoa powder, baking powder, and salt.
2 Prepare a double boiler by adding 2-inches of water in a medium saucepan over high heat. Bring to a simmer, then reduce the heat to keep the water at a slow simmer. Add a large glass or metal bowl over top, making sure the fit is snug and the bottom of the bowl does not touch the water.
3 To the large glass bowl, whisk the butter and buttermilk together over the heat until the butter is totally melted. Add the espresso powder (or instant coffee), eggs, and vanilla, then whisk to combine.
4 Pour the wet, combined ingredients into the bowl with the dry ingredients and whisk until smooth. Stir in the chocolate chips.
5 Divide the batter between the two prepared cake pans and bake for 1 hour or until a knife comes out (from the center) clean.
6 While the cakes are in the oven, make the frosting. To do this, you’ll need to add all of the ingredients to a stand mixer with a whisk attachment. Starting on low speed, mix the ingredients until combined, then increase the speed to medium-high speed and mix until smooth.
7 Let the cakes cool for 30 minutes in the pan, then transfer them to a wire rack (run knife along sides and then flip over to remove from pan).
8 Let the cakes cool completely on the wire rack, then ice or frost as desired.
