Heat oven to 450 degrees. In a large mixing bowl, stir together flour, sugar, baking powder and salt until combined. Add the grated butter and stir just until the butter is incorporated and coarse crumbs appear throughout the dough.
Pour buttermilk on top of flour mixture. Stir just until combined -- you don't want to overwork the dough. The dough will look crumbly, but it will come together in the next steps.
Turn the dough out onto a floured surface, like a countertop or pastry board. Gently using your hands, combine the dough so that it comes together and then pat the dough into a 1-inch-thick rectangle. If necessary, you can flour your hands to work with the dough if it's a bit sticky.
Fold one side of the dough toward the center, and then fold the other side on top of the first fold like a letter. Flatten into a 1-inch-thick rectangle again and then give it a quarter turn. Repeat three more times and flatten into the final 1-inch-thick rectangle. (Please see the blog for photos if that's helpful.)
Using a 3-inch cookie cutter, cut the dough into shortcakes. Do not twist the cookie cutter. Simply press down, lift straight up and gently remove the dough. Reshape the scraps and cut more shortcakes. This recipe should yield about six shortcakes.
Place the shortcake dough close together in a 12-inch cast-iron skillet. Alternatively, you can use a baking pan, but the cast-iron skillet will give you a nice crust. Brush with additional buttermilk and bake until the tops start to brown, about 15 minutes.