Bloom: Pour the hot brewed coffee directly into the batter. Whisk gently until smooth and uniform. Note: The batter will be very thin.
Bake: Divide the batter evenly between the two pans. Bake for 30 to 35 minutes, until a toothpick inserted into the center comes out clean. Cool in the pans for 10 minutes, then turn out onto a wire rack to cool completely.
Make the chocolate fudge frosting
Combine chopped chocolate, butter, heavy cream, and sifted powdered sugar in a medium saucepan over the lowest heat setting. Whisk constantly until smooth, melted, and glossy.
Strain through a fine mesh sieve into a shallow dish to remove any air bubbles.
Place the frosting in the fridge until it thickens to a spreadable, fudgy consistency.
Assembly
Place the first cooled cake layer on a serving plate or turntable. Spread a generous layer of the fudge frosting evenly over the bottom layer using an offset spatula. Top with the second cake layer.
Spread the remaining fudge frosting smoothly over the top and sides of the entire cake, smoothing the top with your spatula for a sleek, glossy finish.
Let the cake sit at room temperature for 15 minutes before slicing to allow the frosting to settle.
Notes
Measuring Accuracy: For the best results, measure the flour and cocoa powder with a digital kitchen scale. Scooping directly with measuring cups can pack in extra flour, resulting in a dry sponge.
Ingredient Temperatures: Use room temperature eggs and buttermilk so the wet ingredients blend smoothly without seizing the vegetable oil.
Blooming Cocoa: Ensure the brewed coffee is steaming hot when added to the batter. The heat dissolves the cocoa solids instantly to unlock maximum flavor.
Pan Preparation: Grease the cake pans thoroughly and line the bottoms with parchment paper rounds to guarantee the cake layers release cleanly.
Gentle Heat for Frosting: Melt the dark chocolate, butter, heavy cream, and powdered sugar on the lowest stove setting while stirring constantly. High heat can break the emulsion and make the fudge dull or separated.
Frosting Consistency: Stir the frosting every 10 minutes while it chills in the fridge until it reaches a spreadable texture. If it becomes too firm, set the bowl over a pot of warm water for 1 to 2 minutes to soften.
Serving Temperature: Bring refrigerated cake slices to room temperature 20 to 30 minutes before serving. This softens the fudge frosting and restores the ultra-moist texture of the cake layers.