Sift flour, baking powder and salt into a medium sized bowl.
Cream together butter and both sugars until light and fluffy, scraping down bowl with a rubber spatula as needed. Add egg and beat well. Stir in vanilla.
Add flour mixture, and beat into butter mixture on low speed.
Prepare two pieces of parchment paper with a dusting of flour, and roll out half of the dough onto each parchment. Place the parchment paper with the dough on a baking sheet and completely cover with plastic wrap. Refrigerate for at least 2 hours, or overnight.
When ready to cut the cookie shapes and bake them, preheat the oven to 350℉. Remove one sheet of the rolled out dough on the parchment paper from the baking sheet and place it on the counter or a cutting board. Place a new piece of parchment paper on the baking sheet.
Cut out the cookie shapes and place them onto the prepared pan. Gather up any extra dough and re-roll to continue to cut as many cookies as possible. With the last bit of dough, I usually just make a flat round cookie.
Bake them cookies for about 10-12 minutes, or until golden brown and dough is set. Remove from oven and cool for about 10 minutes before placing them on a rack for decorating. Repeat the process with the second batch of dough.