Preheat your oven to 350ºF and prepare your cupcake pan with paper liners.
For the best results, warm the buttermilk in the microwave (roughly 100ºF), bring the butter to room temperature, and warm the eggs in hot water for 5 minutes. Warm ingredients will create an emulsion and a smoother batter.
Combine the buttermilk, oil, and vanilla together and set it aside.
Whisk together the flour, cocoa powder, baking soda, baking powder, salt, and espresso powder in a mixing bowl and set it aside.
Cream together the butter, white sugar and sifted brown sugar in your stand mixer with the paddle attachment until light and fluffy. If you don't have a stand mixer, you can use the whisk attachment and a hand mixer, but I would mix the rest of the ingredients by hand to avoid overmixing.
Add in the eggs one at a time while mixing on low, letting the first one mix in before adding the second. Scrape the bowl to be sure that everything is mixed well.
While mixing on low speed, add ⅓ of the dry ingredients, followed by ⅓ of the wet ingredients. Alternate two more times until just combined.
Fill your cupcake liners ½ to ⅔ of the way full. This recipe makes about 24 cupcakes.
Bake the cupcakes at 350°F for 18-20 minutes until set. Do not over bake.
Cool completely on a cooling rack before frosting.