Preheat oven to 350°F (175°C) and line a muffin tin with paper liners.

In a medium bowl, whisk together flour, baking powder, and salt until combined.

In a large mixing bowl, cream butter and sugar until light and fluffy, about 2-3 minutes.

Add eggs one at a time, mixing well, then stir in vanilla extract until smooth.

Gradually add dry ingredients to wet ingredients, alternating with milk, mixing just until combined.

If using, fold in sour cream or yogurt until incorporated.

Fill muffin liners about ⅔ full and bake for 18-22 minutes until golden.

Let cupcakes cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.

Prepare frosting by beating butter and powdered sugar together with vanilla and milk until fluffy.