Preheat the oven to 350°F (175°C). Grease and flour a 9-inch round cake pan.
In a medium bowl, whisk together the flour, baking powder, and salt; set aside.
In a large bowl, cream the butter and sugar together until light and fluffy.
Add the eggs one at a time, beating well after each addition.
Stir in the limoncello and vanilla extract.
Gradually mix in the flour mixture alternately with the milk, starting and ending with flour.
Fold in the lemon zest until just combined.
Pour the batter into the prepared cake pan and spread evenly.
Bake in the preheated oven for 30-35 minutes, or until a toothpick inserted into the center of the cake comes out clean.
Let the cake cool in the pan for 10 minutes, then turn it out onto a wire rack to cool completely.