Preheat your oven to 350°F (175°C). Line a cupcake tin with paper liners.
In a medium bowl, whisk together the flour, baking powder, and salt.
In a large bowl, beat the butter and sugar together until light and fluffy. Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract.
Gradually add the flour mixture to the butter mixture, alternating with the milk, beginning and ending with the flour mixture. Mix until just 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 cupcakes to cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.
For the frosting, beat the butter until creamy. Gradually add the powdered sugar and cocoa powder, mixing until smooth. Add the vanilla extract and milk, and beat until fluffy.
Frost the cooled cupcakes with the milk chocolate frosting.