Preheat oven to 350°F. Line muffin tins with 24 cupcake cases.
Combine flour, sugar, cocoa powder, baking soda, and salt. In a separate bowl, whisk together coffee, vegetable oil, buttermilk, and eggs. Add dry mixture to wet mixture and whisk until smooth. Pour into cupcake cases and bake for 20-25 minutes. Cool completely.
Whip butter for 3-5 minutes until light and fluffy. Add powdered sugar in two parts, mixing well after each addition. Add two tablespoons each coffee and cocoa powder and mix thoroughly. Add more of either if desired. Mix for one more minute and cover with cling film in the fridge until use.
Grab your cupcakes and frosting. Frost them however you like and place one coffee bean on the top of each cupcake.