Mix together all the dry ingredients. Stir in the frozen grated butter. See how it says "frozen grated" there? That means freeze the butter. Then grate the frozen blob of butter. Then freeze the grated butter. It's really important to keep the butter from melting while it's being stirred into the mix, because the tiny bits of butter melting in the over make the biscuits flaky.

Then fold in enough cold buttermilk to make a dough ball that just sticks together. (Add more buttermilk if needed.)

Turn out onto a floured surface, and roll out into a rectangle. Fold the rectangle into thirds, turn, and roll out another rectangle. Do this 5 or 6 times.

Cut into rounds, press the center of each one with your thumb. Brush with buttermilk if desired. Bake at 425F for 15 minutes.