Preheat the oven to 350 degrees F. Line a muffin tin with paper liners.

Whisk to combine the flour, cocoa powder, sugar, baking soda, baking powder, and salt. Set aside.

In another bowl, whisk to combine the buttermilk, oil, egg, and vanilla. Slowly pour the wet ingredients into the dry while stirring, and before the flour has disappeared into the batter, stir in the coffee.

Evenly divide the batter into the muffin cups, filling them no more than 3/4 full.

Bake for 22 minutes, until a toothpick inserted into the center comes out clean. Let the cupcakes cool completely on a wire rack.

To make the buttercream, beat all buttercream ingredients in a bowl until smooth and blended, about 3 minutes on high speed.

Pipe the buttercream onto the cupcakes as desired. Optional: drizzle with chocolate syrup and sprinkle with chopped peanuts.