Preheat the oven to 350?F (175?C) and line a muffin tin with cupcake liners.

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

Add the eggs one at a time, mixing well after each addition.

Stir in the lemon juice and lemon zest.

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

Gradually add the dry ingredients to the wet ingredients, alternating with the milk, and mix until just combined.

Divide the batter evenly among the cupcake liners, filling each about 2/3 full.

Bake for 18-20 minutes, or until a toothpick inserted into the center comes out clean.

Allow the cupcakes to cool completely before frosting.

In a mixing bowl, beat the softened butter until creamy.

Gradually add the powdered sugar, mixing until well combined.

Add the lemon juice and lemon zest, and mix until smooth. If the frosting is too thick, add a little milk to reach desired consistency.

Frost the cooled cupcakes with the lemon buttercream frosting.