Preheat oven to 350°F (177°C). Line two 12-count muffin pans with 16 cupcake liners and set aside.
In a large mixing bowl, sift together the flour, cocoa powder, baking powder, baking soda, and salt. Whisk in the brown sugar and granulated sugar until well combined. Then whisk in the oil, buttermilk, egg, and vanilla extract and mix until just combined.
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, this is okay.
Evenly distribute the batter between all 16 cupcake liners, making sure to fill each one a little over halfway full. Bake in separate batches at 350°F (177°C) for 16-18 minutes or until a toothpick inserted into the center of the cupcakes comes out clean.
Remove from the oven and carefully remove the cupcakes from the pans, then transfer to a wire rack to cool completely.