1. Preheat oven to 475°. Grate frozen butter using large holes of a box grater. Toss together grated butter and flour in a medium bowl. Chill 10 minutes.
2. Make a well in center of mixture. Add buttermilk, and stir 15 times. Dough will be sticky.
3. Turn dough out onto a lightly floured surface. Lightly sprinkle flour over top of dough. Using a lightly floured rolling pin, roll dough into a 3/4-inch-thick rectangle (about 9 x 5 inches). Fold dough in half so short ends meet. Repeat rolling and folding process 4 more times.
4. Roll dough to 1/2-inch thickness. Cut with a 2 1/2-inch floured round cutter, reshaping scraps and flouring as needed.
5. Warm a cast-iron skillet in the oven, and spread a bit of butter in the skillet before adding the biscuits. Place dough rounds in skillet. Bake at 475° for 15 minutes or until lightly browned. Brush with melted butter.