Preheat your oven to 350°F (175°C) and line a muffin tin with cupcake liners.
In a mixing bowl, cream together the butter and sugar until light and fluffy.
Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract.
In another bowl, whisk together the flour, baking powder, and salt. Gradually add to the butter mixture, alternating with the milk, beginning and ending with the flour mixture.
Divide the batter evenly among the cupcake liners, filling each about two-thirds full.
Bake for 18-20 minutes, or until a toothpick inserted into the center comes out clean. Cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.
For the frosting, melt the butter in a saucepan over medium heat. Stir in the brown sugar and milk. Bring to a boil and cook for 1 minute, then remove from heat and let cool slightly.
Gradually beat in the powdered sugar until smooth and spreadable. Frost the cooled cupcakes with the caramel frosting.