Step 1

Arrange a rack in the middle of the oven and heat to 350°F. Coat the wells of a 12-cup muffin pan with cooking spray or line with paper liners.

Step 2

Whisk the sugar, flour, cocoa powder, baking powder, baking soda, and salt together in the bowl of a stand mixer fitted with the paddle attachment. (Alternatively, use an electric hand mixer and large bowl.) Add the egg, milk, oil, and vanilla. Beat on medium speed until well-combined, about 2 minutes. Beat in the hot coffee. The batter will be quite thin. Divide the batter evenly between the wells in the pan, filling each no more than 3/4 full.

Step 3

Bake until a toothpick inserted in the center of the cupcakes comes out clean, 15 to 18 minutes. Cool the cupcakes in the tin for about 5 minutes, then transfer to a cooling rack to cool completely. Meanwhile, make the frosting.

Step 4

Place the butter and fluff in the clean bowl of a stand mixer fitted with the paddle attachment. (Alternatively, use an electric hand mixer and clean bowl.) Beat until light and fluffy, about 2 minutes. Slowly add the powdered sugar while beating over low speed until incorporated. Beat in the vanilla.

Step 5

Frost the cooled cupcakes with a knife, or transfer the frosting to a pastry bag fitted with a round tip and pipe onto the cupcakes.