Add buttermilk, vegetable oil, egg, and vanilla to dry mixture on medium speed until well combined.
1 cup buttermilk, 1/2 cup vegetable oil, 2 large eggs, 2 teaspoons vanilla extract
Reduce speed and carefully add boiling water to the cake batter. Beat on high speed for about 1 minute to add air to the batter.
Fill each cupcake liner 1/2 way full. Depending on the size of cupcake liners you use, you will need to use more or less. Be sure not to over fill.
Bake until a toothpick inserted in the center comes out clean, about 20 minutes
Remove from the oven and allow the cupcakes to cool completely on a wire rack.
Instructions for the chocolate buttercream frosting:
While cupcakes cool, make the buttercream frosting.
Add cocoa to bowl of stand mixer. Using a whisk or fork, get rid of any lumps.
1 cup unsweetened cocoa
Add butter to the cocoa. Cream butter and cocoa powder until combined. Turn off mixer.
1½ cups butter
One cup at a time, add in the confectioner’s sugar and about a teaspoon of the cream. Slowly bring mixer up to speed to avoid the sugar from flying out of the bowl. Between each addition, bring up to fast speed to fully whip the frosting. Repeat until all the sugar and cream are added.
5 cups confectioner’s sugar, 1/4 cup heavy cream
Add vanilla extract and espresso powder and combine well.
2 teaspoons vanilla extract, ½ teaspoon espresso powder
At this point, check the consistency of the frosting. If too stiff, add a bit more of the cream, and beat until fluffy.
Using a piping bag, pipe swirls onto the cooled cupcakes. You may also frost with butter knife.
Notes
Cupcakes can be stored in a refrigerator for up to 2 weeks. Be sure to allow to come to room temperature before serving.