Preheat oven, line tin:

Set oven to 350°F (175°C). Place paper liners in a 12-cup muffin tin.

Beat wet ingredients:

In a large bowl, use an electric hand mixer to combine the egg, oil, white sugar, brown sugar, coffee, milk, and vanilla extract. Beat for 1-2 minutes until smooth.

Sift dry, fold batter:

In another bowl, sift together the flour, cocoa powder, baking powder, baking soda, and salt. Add the wet mixture to the dry ingredients and fold gently until just incorporated; avoid overmixing.

Fill cupcake liners:

Distribute the batter evenly among the lined cups, filling each around 3/4 full.

Bake and cool cupcakes:

Bake for 20-22 minutes, or until a toothpick inserted in the center emerges clean. Do not overbake. Transfer to a wire rack and let cool completely to room temperature before applying frosting.

Beat butter until fluffy:

In a stand mixer or using an electric hand mixer in a large bowl, beat the softened butter on medium-high speed for 3 minutes until light and airy.

Add sugar, beat frosting:

Lower the speed to low and slowly add the powdered sugar, one tablespoon at a time. After all sugar is incorporated, raise the speed to medium-high and beat for 4 minutes until fluffy and increased in volume.

Dissolve espresso in cream:

In a small bowl, mix the espresso powder into the heavy cream until completely dissolved.

Mix in cream mixture:

With the mixer on low, add the vanilla extract, salt, and the cream-espresso mixture. Beat for 1 minute until smooth and creamy.

Pipe frosting onto cupcakes:

Fill a piping bag fitted with a nozzle with the frosting. Pipe onto the cooled cupcakes. Garnish as desired, such as with coffee beans or a dusting of cocoa powder.

Serve or refrigerate:

Serve immediately. Keep leftovers in an airtight container in the refrigerator for 2-3 days. Allow to come to room temperature before serving to soften the frosting.