Whisk the flour, baking powder, and salt together in a medium bowl. Combine ¼ cup of the limoncello with the milk. Beat the butter in a large bowl with an electric mixer on high speed until creamy, about 1 minute. Gradually beat in the sugar and continue beating until the mixture is light in color and texture, about 3 minutes. (Or cream the butter and sugar well by hand.) One at a time, beat in the eggs, letting the first egg be absorbed before adding the next. Mix in the vanilla and lemon zest. With the mixer on low speed, In thirds, beat in (or stir in by hand) the flour mixture, alternating with two equal additions of the milk mixture, beating until smooth after each addition and scraping down the sides of the bowl as needed. Scrape the batter into the cake pan and smooth the top.