Pulse 1 1/2 cups flour, 1 tablespoon baking powder and 1 teaspoon salt in a food processor until combined. Pulse in 6 tablespoons cold unsalted butter until pea-size. Pulse in 2/3 cup buttermilk and 2 tablespoons chopped chives. Pat into a 6-inch square on an ungreased baking sheet; score into 12 biscuits. Brush with buttermilk. Bake at 425 degrees F until browned, 25 minutes. Cool slightly; cut into biscuits.