Make the Cake
Preheat the oven:
Preheat to 350°F (175°C). Grease and line two 8-inch round cake pans with parchment paper.
Mix dry ingredients:
In a large bowl, whisk together flour, cocoa powder, baking powder, baking soda, and salt.
Combine wet ingredients:
In another bowl, whisk melted butter, both sugars, eggs, buttermilk, and vanilla until smooth.
Combine and add coffee:
Slowly mix dry ingredients into wet until just combined. Pour in hot coffee and stir until the batter is silky and smooth.
Bake:
Divide batter evenly into pans. Bake for 25–30 minutes, or until a toothpick inserted comes out with moist crumbs.
Cool:
Let cakes cool for 10 minutes in the pan, then transfer to wire racks to cool completely.
Make the Fudge Frosting
Heat heavy cream and butter in a small saucepan until just simmering.
Pour over chocolate chips in a bowl and let sit for 2 minutes.
Stir until smooth, then add vanilla and powdered sugar.
Whisk until thick, glossy, and spreadable.
Assemble the Cake
Place one cooled cake layer on a plate or stand.
Spread a layer of fudge frosting evenly across the top.
Add the second cake layer and cover the top and sides with remaining frosting.
Chill for 30 minutes before slicing for perfect, clean layers.