Preheat your oven to 350°F.
Add the flour, sugar, cocoa powder, baking soda, baking powder, salt, and espresso powder into the bowl of a stand mixer equipped with a whisk attachment. Whisk until all ingredients are combined.
Add the milk, vegetable oil, eggs, vanilla extract, and Guinness into the dry ingredients and mix until there are no dry spots. Do not overmix.
Evenly divide the batter between 16 cupcake liners and bake at 350°F for 15-16 minutes or until a toothpick inserted in the center of the cupcakes comes out clean.
Allow to cool for 5 minutes in the pan then remove to a wire rack to cool completely.