Whisk together flour, baking powder, and salt in a large bowl. Beat butter and granulated sugar with a mixer on medium-high speed until pale and fluffy. Beat in egg and citrus zest and juice. Reduce speed to low. Add flour mixture, and beat until combined. Proceed with variations:Thumbprints and Ball Cookies Shaped Icebox Cookies Layered Icebox Cookies Glazed Spritz Cookies Cutout Cookies
Dough can be refrigerated overnight or frozen for up to 1 month.