• Preheat the oven to 350 degrees F and place the oven rack in the center of the oven.
• Butter, or spray with a non-stick vegetable spray, two 9-inch cake pans. Then line the bottoms of the parchment paper.

  Or use Pan Coat and Silicone Baking Pans
• Whisk together the sugar, flour, cocoa powder, baking powder, baking soda, and salt in a large bowl.
• Whisk together the eggs, coffee, milk, oil, and vanilla extract in a separate bowl. Add the wet ingredients to the dry ingredients and stir until combined. (The batter will be runny.)
• Pour the batter into the prepared cake pans and bake for about 27-32 minutes or until a toothpick inserted into the center of the cake comes out clean.
• Remove from the oven and let cool for about 10 minutes. Then remove the cakes from their pans and cool completely on a greased wire rack before frosting.

For the frosting

• Melt the chocolate in a heatproof bowl placed over a saucepan of simmering water. Remove from heat and let cool to room temperature.
• Beat the butter until smooth and creamy (about 1 minute).
• Add the sugar and beat until it is light and fluffy (about 2 minutes).
• Beat in the vanilla extract. Add the chocolate and beat on low speed until incorporated.
• Increase the speed to medium-high and beat until the frosting is smooth and glossy (about 2-3 minutes)
• Add the sour cream and mix until smooth and combined.