Preheat oven to 350 degrees. Line muffin pan with cupcake liners and set aside.
Whisk together cocoa and espresso powder in medium sized bowl. Add boiling water and set aside.
In a seperate bowl, whisk flour, sugar, baking powder, baking soda and salt. Set the bowl aside.
Combine eggs, oil, sour cream, and vanilla at low speed in the bowl of an electric mixer.
Turn off the mixer and add the cocoa mixture and dry ingredients to the egg mixture. Turn the mixer on low speed to blend the ingredients. Increase the speed on the mixer to medium-high speed and beat for 2 minutes to create a smooth cake batter.
Using large cookie scoop, add two scoops of batter to each cupcake liner.
Bake for 22-24 minutes or until wooden toothpick comes out clean.