Use all of the ingredients in Joshua Russell's buttercream recipe found in the materials section of the Craftsy Modern Buttercream course with the exception and addition noted below.
Exception: 2 teaspoons vanilla extract instead of 2 tablespoons
Follow the instructions in Joshua Russell's buttercream recipe, making the change to the vanilla quantity noted above and mixing in the instant coffee at the very end.
Fudge Swirl and Topping Instructions
Using a food-safe brush, paint a stripe of fudge inside a piping bag fitted with an open star tip.
Fill the bag with mocha frosting and pipe onto cooled cupcakes. As you pipe, you'll see a swirl of fudge appear throughout the frosting.