Preheat oven to 350°F (175°C). Line a cupcake tin with paper liners.
In a large bowl, whisk together flour, sugar, cocoa powder, baking powder, baking soda, and salt.
Add milk, vegetable oil, vanilla extract, and egg. Beat until well combined.
Divide the batter evenly among the cupcake liners, filling each about ⅔ full.
Bake for 18-20 minutes, or until a toothpick inserted into the center comes out clean. Allow to cool completely.
For the frosting, beat butter and cocoa powder together until smooth. Gradually add powdered sugar, milk, and vanilla extract. Beat until fluffy.
Frost the cooled cupcakes with the fudge frosting.