1. Line a 12-cup muffin tin with paper liners. Set aside. Preheat the oven to 350°F.
2. In a medium bowl, whisk together the flour, sugar, cocoa, baking soda, and salt. Set aside.
3. In a small bowl, whisk together the eggs, cold coffee, oil, vinegar, and vanilla. Add to the dry ingredients and mix well.
4. Fill each paper-lined cup three-quarters full. Bake for 20–25 minutes, or until a toothpick inserted in the center comes out clean.
5. Cool for 10 minutes in the pan, then transfer to a wire rack to cool completely to room temperature before frosting.

Mocha Frosting

1. Beat the butter in a stand mixer on medium-high until pale and creamy, about 2 minutes.
2. Add the sifted powdered sugar, cocoa powder, vanilla, and a pinch of salt. Mix on low to incorporate, then increase to medium-high and beat for 2 minutes until fluffy.
3. Add the cooled coffee or espresso one tablespoon at a time, beating between additions, until the frosting reaches a smooth, pipeable consistency. Taste and adjust — add more coffee for stronger mocha flavor or more sugar to sweeten.
4. Pipe the frosting onto the cooled cupcakes using a star tip or large round tip. Top each with a chocolate-covered espresso bean if desired.