Place cupcake liners in muffin tin. Spray lightly with cooking spray.
Add flour, sugar, cocoa, baking powder, baking soda, salt and espresso powder to a large bowl or the bowl of a stand mixer. Whisk through to combine or, using your paddle attachment, stir through flour mixture until combined well.
Add milk, vegetable oil, egg, and vanilla to flour mixture and mix together on medium speed until well combined. 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.
Evenly distribute cake batter. Each cupcake liner should be about 1/2 full.
Place in the oven and 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.