2. Make the Frosting
Melt the chopped chocolate in a heatproof bowl set over a pot of barely simmering water, stirring until smooth. Remove from heat and let cool until just warm to the touch.
In a large bowl, beat the softened butter until creamy. Beat in the cooled, melted chocolate until combined.
Add half of the confectioners’ sugar, all of the sour cream, vanilla, and salt. Beat on low until combined, then increase speed to medium-high and beat for 1 minute.
Add the remaining confectioners’ sugar and beat on low until incorporated, then on medium-high for another 1-2 minutes until the frosting is smooth, fluffy, and spreadable.
3. Assemble the Cake
Place one cooled cake layer on a serving plate or cake stand. Spread a generous layer of frosting evenly over the top. Top with the second cake layer.
Spread the remaining frosting over the top and sides of the cake, swirling decoratively.
Baker’s Notes
Secret Ingredient: The hot coffee intensifies the chocolate flavor without making the cake taste like coffee. It’s essential for the signature moist texture.
Room Temperature is Key: Using room-temperature milk, eggs, and sour cream ensures a smooth batter and frosting without curdling.
Frosting Consistency: If the frosting is too soft, chill it for 15 minutes. If it’s too thick, add a teaspoon of milk or more sour cream.
Serve at room temperature with a tall glass of cold milk. Store covered at room temperature for 2 days, or refrigerate for up to 5 days.
