#### 1. Prepare the pans and oven
Preheat the oven to 350°F (175°C). Butter (or spray) two 8-inch or 9-inch round cake pans. Line the bottoms with parchment paper circles, then butter and flour the paper for easy release.
#### 2. Mix the dry ingredients
In a large bowl (or the bowl of a stand mixer), whisk together the flour, sugar, cocoa powder, baking soda, baking powder, and salt until well combined.
#### 3. Combine wet ingredients
In a separate bowl or large measuring cup, whisk the buttermilk, vegetable oil, eggs, and vanilla extract. Pour the wet mixture into the dry ingredients, mixing on low speed (or whisking by hand) until just combined.
#### 4. Add coffee and finish the batter
Slowly pour in the hot coffee (or hot water) while mixing on low speed. Scrape down the sides and bottom of the bowl to ensure the batter is fully incorporated. The batter will be quite thin—this is normal.
#### 5. Bake
Divide the batter evenly between the prepared cake pans. Bake for 25–35 minutes, or until a toothpick inserted into the center comes out with just a few moist crumbs (not wet batter). Cool the cakes in their pans for 10 minutes. Run a knife around the edges to loosen, then invert them onto cooling racks. Peel off the parchment and let them cool completely.
#### 6. Make the chocolate frosting
Melt the chopped chocolate in the microwave in 20-second increments, stirring frequently, or use a double boiler. Let it cool slightly. In a stand mixer (or using a hand mixer), beat the softened butter on medium speed until smooth. Add the cooled, melted chocolate and continue mixing until combined. Beat in the vanilla extract and salt. Gradually add the confectioners’ sugar, mixing on low to avoid spattering. If the frosting is too thick, drizzle in milk or cream, 1 tablespoon at a time, until the desired consistency is reached.
#### 7. Frost the cake
Place one cake layer on a serving plate or cake stand. Spread a layer of frosting on top. Gently place the second cake layer over the first. Frost the top and sides of the cake, smoothing the frosting with an offset spatula or knife.