01 - Preheat oven to 350°F. Line a 12-cup muffin tin with paper liners.
02 - In a medium bowl, whisk together flour, baking powder, and salt until well blended.
03 - In a large bowl, beat butter and sugar until light and fluffy, approximately 2-3 minutes.
04 - Add eggs one at a time, beating well after each addition. Mix in lemon zest, lemon juice, Limoncello, and vanilla extract until fully incorporated.
05 - Add dry ingredients in three parts, alternating with milk, beginning and ending with dry ingredients. Mix until just combined; avoid overmixing.
06 - Divide batter evenly among cupcake liners, filling each approximately 2/3 full.
07 - Bake for 18-20 minutes, or until a toothpick inserted into the center comes out clean. Cool in pan for 5 minutes, then transfer to wire rack to cool completely.
08 - Beat butter until creamy. Gradually add powdered sugar, beating until smooth. Add Limoncello, lemon juice, lemon zest, and salt; beat until light and fluffy, approximately 2-3 minutes.
09 - Frost completely cooled cupcakes with Limoncello frosting. Decorate with additional lemon zest if desired.