Preheat oven to 350°F (175°C). Line a muffin tin with cupcake liners.

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

In a large bowl, cream together the softened butter and granulated sugar until light and fluffy.

Beat in the eggs one at a time, then stir in the vanilla extract and lemon zest.

In a small bowl, whisk together the milk and lemon juice.

Alternately add the dry ingredients and the milk mixture to the butter mixture, beginning and ending with the dry ingredients. Mix until just combined.

Fill cupcake liners about two-thirds full with batter.

Bake for 20-25 minutes, or until a toothpick inserted into the center comes out clean.

Let the cupcakes cool in the tin for a few minutes before transferring them to a wire rack to cool completely.

In a large bowl, beat together the softened butter until creamy.

Gradually add the powdered sugar, alternating with the lemon juice, until smooth and creamy.

Stir in the lemon zest.

Once the cupcakes are completely cool, frost them with the lemon frosting.