Step 1

Preheat oven to 350°F. Grease 6 muffin cups or place 6 liners in a muffin pan. Set aside.

Step 2

With a stand mixer or hand mixer, combine sugar, flour, cocoa powder, baking powder, baking soda, and salt. Add egg, milk, oil, and vanilla extract and beat for 2 minutes. Add hot coffee or hot water, and beat until just combined. Batter will be thin.

Step 3

Divide evenly between 6 prepared muffin cups. Bake for approximately 15 minutes, until the tops spring back when you touch them, and a toothpick inserted into the center comes out clean. Transfer the pan to a wire rack to cool completely.

Step 4

Beat butter and powdered sugar for several minutes, until smooth. Add vanilla extract and milk, and beat for several more minutes, until light and fluffy. If the frosting seems a little too thick, beat in a splash of milk. If it seems too thin, add another tablespoon of powdered sugar.

Step 5

Frost the cooled cupcakes using a decorating tip or a butter knife. Garnish with sprinkles, if desired.