Heat the oven to 400° and coat two baking sheets with cooking spray. In a small bowl, whisk together 2 3/4 cups flour, the baking powder, and the salt. In a stand mixer set on medium speed, beat together the butter and confectioners' sugar until fluffy. Reduce the mixer's speed to low, add the egg, lemon juice, and lemon zest, and blend until well incorporated. Add the flour mixture and blend until a soft dough forms. Add more flour, a tablespoon at a time, if the dough is sticky.