In a mixing bowl, cream the butter until soft, smooth, and fluffy.
Gradually add the powdered sugar and beat until smooth.
In another bowl, combing the flour, salt, and baking powder.
Add the flour mixture to the butter mixture and stir until combined.
On a clean, floured surface, roll out the dough into a 1/4-inch thick circle.
Cut the shortbread into shapes and place on an ungreased baking sheet, about 1/2-inch apart. Prick each cookie with a fork and sprinkle a little sugar over the tops.
Bake for 20-25 minutes, or until light brown around the edges.
Cool on a rack and enjoy!
Notes:
Make Ahead: You can easily make these early in the day, or make them several days in advance and freeze them.