Preheat oven to 450 degrees with rack in middle of oven
Whisk the flour, baking powder, baking soda, and salt together in a bowl, set aside
Place a box grater over a small piece of parchment paper. Grate the frozen butter on the large holes of a box grater. When you get down to a small nub of better, chop it into 4-5 small pieces.
Use the piece of parchment paper to transfer the butter to the dry ingredients. Use your fingers to sift the butter into the flour and break up any clumps of grated butter.
Pour in the buttermilk and beat it in with a wooden spoon until the dough comes together and pulls away from the sides of the bowl.
Transfer the dough to a lightly floured cutting board. Pat the dough into a 1 inch thick rectangle. Sprinkle the dough with at little more flour, if needed. Fold the dough in half from top to bottom, than pat it back down into its original shape. Repeat with the folding and patting, alternating folding from each side, the bottom, and the top until you have completed a total of 8 folds. At the end, the dough should be a little springy to the touch.
Pat the dough into a 1-inch thickness. Use a 3-inch round cutter to cut the dough into 6 biscuits. If you don't get 6 the first time, refold and put down excess dough and cut more. Discard scraps.
Arrange the biscuits in a 10-inch cast iron skillet, so the biscuits touch one another, but not the sides of the pan. Increase oven temp to 500 degrees and bake until biscuits are golden-brown for 15-18 minutes.