Preheat the oven to 350. Line a baking sheet with a parchment or silicone liner and set aside. In a medium bowl, beat together the butter and sugar until light and fluffy. Add the egg and vanilla and mix until smooth. Add the flour, baking powder, and salt, and mix until combined. Chill for 20-30 minutes, until firm. Using a teaspoon or a small cookie scoop, roll the dough into small balls. Flatten slightly and place on the prepared baking sheet. Bake 15-17 minutes, until golden brown.