Preheat oven to 350ºF. In a medium-sized bowl, whisk together the flour, baking powder, and salt. Set aside.

In a large bowl, use a handheld electric mixer to beat the butter on medium speed for 2 minutes, until creamy. Add the sugar and beat on medium speed for 2 more minutes. Add the egg, egg yolk, and vanilla and beat on low speed until combined. Add the dry ingredients and use a spatula to combine.

Cover the bowl of cookie dough with plastic wrap and chill the dough for at least 1 hour in the refrigerator. Once chilled, roll the dough into equal-sized balls and roll each one in sugar (if desired). Place cookies on a baking sheet and bake at 350ºF for 11-12 minutes.