Preheat oven to 350°F. Line a baking sheet with parchment paper and set aside.
In food processor, combine flour, sugar, baking powder and salt. Add cold butter and pulse until pea-sized crumbs form. Pour into a large mixing bowl.
In a separate bowl (or liquid measuring cup) combine buttermilk, egg, and vanilla.
Stir cookies into flour mixture. Next add buttermilk mixture to flour mixture, folding until combined and dough forms a ball.
Put dough on prepared cookie sheet and press to form a 9-inch circle. Sprinkle the top with sugar, if desired. Bake for 25 minutes, or until a toothpick inserted in the center comes out clean. Cut into 8 to 10 wedges (a pizza cutter works well for this).
