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 limoncello and lemon zest.

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

Gradually add the dry ingredients to the wet ingredients, alternating with the buttermilk, starting and ending with the dry ingredients.

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

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

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

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 and fluffy.

If the frosting is too thick, add a tablespoon of milk to reach desired consistency.

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

Optionally, garnish with additional lemon zest or a slice of lemon on top.