Preheat the oven to 350 degrees F. Line 2 baking sheets with parchment paper or silicone baking mats and set aside.
Using an electric mixer, beat the butter and granulated sugar until the mixture is light and fluffy. Add the egg yolks, limoncello, vanilla and lemon zest, and beat until combined.
In a separate medium bowl, combine the flour, baking powder, and salt.
Add the flour mixture to the butter mixture all at once and mix again with electric mixer until a soft dough forms. Use a spoon to mix the dough to bring the dough together more fully.
Use a medium cookie scoop (about 1 ½ tablespoons of dough) to scoop the dough and roll into balls and place them on the prepared baking sheet about 2-inches apart. Use the palm of your hand to slightly flatten the balls of dough.
Bake the cookies for 10 to 12 minutes, or until the bottom edges are just beginning to look golden brown. Remove from the oven and allow to cool on the baking sheets for 10 minutes before transferring to wire racks to cool completely.