How to Make It
Preheat oven to 425°F. Line a baking sheet with parchment paper.
Stir together flour and sugar in a large bowl. Using 2 forks or a pastry blender, cut in cold butter until mixture is crumbly. Stir in cold buttermilk until a shaggy dough forms.
Turn out dough onto a lightly floured surface. Pat dough into a rectangle, and cut into fourths. Stack each fourth on top of each other, and pat into a rectangle again. Repeat cutting and stacking procedure. Roll dough into a 10- x 8-inch rectangle about 3/4 inch thick. Cut into 15 (2- x 21/2-inch) rectangles. Arrange rectangles about 1/4 inch apart on prepared baking sheet. Freeze until cold, about 10 minutes. Brush with egg; sprinkle with salt, if desired.
Bake in preheated oven until golden brown, about 15 minutes. Let cool 5 minutes; serve warm.
Substitute self-rising flour with an equal amount of all-purpose flour plus 2 tablespoon granulated sugar, 1 tablespoon kosher salt, 1 tablespoon baking powder, and 1/2 teaspoon baking soda.