Step 1

Preheat the oven to 350°F (177°C). Line two 12-count muffin pans with 16 cupcake liners and set aside.

Step 2

In a large mixing bowl, sift together the flour, cocoa powder, baking powder, baking soda, and salt. Whisk in the granulated sugar and brown sugar until well combined. Add the oil, buttermilk, egg, and vanilla extract and mix until just combined.

Step 3

Add the instant espresso powder to the 1/2 cup boiling water and mix until fully dissolved. Add to the mixing bowl and mix until everything is just combined. The batter will be thin, but this is okay.

Step 4

Evenly distribute the batter between all 16 cupcake liners, making sure to just fill each one a little over halfway full. Bake at 350°F (177°C) for 17-20 minutes or until a toothpick inserted into the center of the cupcakes comes out clean.

Step 5

Remove from the oven and remove the cupcakes from the pan. Transfer the cupcakes to a wire rack to cool completely.

Step 6

In the bowl of a stand mixer fitted with the paddle attachment, or in a large mixing bowl using an electric mixer, beat the butter on medium speed for 1-2 minutes or until smooth.

Step 7

Add the powdered sugar one cup at a time, making sure to mix well after each addition, then add the cocoa powder and mix until fully combined, stopping to scrape down the sides of the bowl as needed. Add the heavy whipping cream, vanilla extract, and salt and mix on medium speed until fully combined.

Step 8

Frost the cooled cupcakes as desired.