Set racks in the upper and lower thirds of the oven and preheat to 425 degrees.
Stir together the flour, sugar, and baking powder in a large bowl. Rub in the butter finely, using your hands or a pastry blender.
Use a fork to beat together the egg and buttermilk. Add them to the flour mixture. Use the fork to gently mix in the liquid, scraping up from the bottom of the bowl, with a movement similar to the one used to fold in egg whites. Continue until all the dry ingredients are evenly moistened.
Scrape the dough onto a floured surface and gently fold it over on itself two or three times.
Cut the dough until four pieces and press each piece into a 5-inch disk. Place the disks on prepared baking sheets. Use a knife to cut each disk into quarters, but don’t separate the quarters.
Bake the scones until they are well risen and deep golden, about 12 to 15 minutes.