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 sugar until light and fluffy.

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

Stir in the buttermilk, lemon juice, and lemon zest until combined.

In another bowl, whisk together the flour, baking powder, baking soda, and salt.

Gradually add the dry ingredients to the wet ingredients, mixing until just combined.

Fill the cupcake liners about 2/3 full with batter.

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

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

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

Gradually add the powdered sugar, mixing until smooth.

Add the lemon juice and lemon zest, mixing until well combined.

If the frosting is too thick, add milk a little at a time until desired consistency is reached.

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

Garnish with additional lemon zest if desired.