Preheat oven to 450°F (230°C). Lightly grease a 9-inch or 10-inch cast iron skillet with butter or shortening.
In a large bowl, add the self-rising flour. Drop in the cold, cubed butter.
Use a pastry blender to cut the butter into the flour until the mixture resembles coarse crumbs with some pea-sized pieces remaining.
Make a well in the center and pour in the cold buttermilk. Gently fold until a shaggy, sticky dough forms. Do not overmix.
Turn the dough out onto a lightly floured surface. Gently pat it into a rough rectangle. Fold the dough in half over itself, turn it a quarter turn, and pat it out again. Repeat this folding process 3 or 4 times.
Pat the dough out to a 3/4-inch to 1-inch thickness. Press a floured biscuit cutter straight down into the dough and pull straight up. Do not twist!
Place the cut biscuits into the prepared skillet so their edges are touching. Gather dough scraps gently to cut remaining biscuits.
Bake for 12 to 15 minutes until the tops are golden brown.
Remove from the oven and immediately brush with the melted butter. Serve warm.