Instructions

• Preheat oven to 350°F. Line a 12-cup muffin pan with cupcake liners.
• In a large bowl whisk together the dry cupcake ingredients: 1 cup and 2 TBSP all-purpose flour, 1/4 cup dark cocoa (regular cocoa will work), 1/3 cup cocoa powder, 1 and 1/4 tsp baking soda, and 1/4 tsp salt. Set aside.
• In a separate bowl whisk the wet cupcake ingredients: 1 large egg plus 1 egg yolk (both at room temperature), 1/2 cup firmly packed brown sugar, and 1/2 cup white sugar until combined.
• Stir 1/2 cup milk and 1/3 cup sour cream into the egg-and-sugar mixture until smooth.
• Stir in 1/3 cup brewed coffee and 1/2 cup melted butter (melted and starting to cool) until combined.
• Pour the wet mixture into the dry ingredients and mix until just combined and no large streaks of flour remain. Do not overmix.
• Divide the batter evenly among the 12 liners, filling each about 3/4 full.
• Bake for 15–20 minutes, or until a toothpick inserted into the center comes out clean and cupcakes spring back lightly when pressed.
• Remove cupcakes from the oven and transfer to a wire rack to cool. Let cool at least 30 minutes, until completely cool, before frosting.
• To make the frosting, beat 1/2 cup butter (softened but not melted) in a bowl until creamy.
• Add 1/3 cup dark cocoa powder to the butter and mix until evenly incorporated.
• Add half of the powdered sugar (1 1/2 cups) and half of the frosting milk (half of the 1/3 cup — use half-and-half or heavy cream as listed). Beat until combined.
• Add the remaining powdered sugar (1 1/2 cups), the remaining frosting milk (the other half of the 1/3 cup), 2 tsp vanilla, and a pinch of salt if desired. Beat on medium-high for 2–3 minutes until the frosting is light and spreadable.
• If the frosting is too thick, add a little more of the same milk (half-and-half or cream) to thin; if too thin, add more powdered sugar to thicken, until you reach the desired consistency.
• Once cupcakes are completely cool, frost them with the prepared chocolate frosting.