In a large mixing bowl beat butter with an electric mixer on medium to high speed for 30 seconds. Add granulated sugar, baking powder, and salt. Beat until combined, scraping sides of bowl occasionally. Beat in egg, milk, and vanilla until combined. Beat in as much of the flour as you can with the mixer. Using a wooden spoon, stir in any remaining flour. Divide dough in half. Cover and chill about 2 hours or until dough is easy to handle.