In a large bowl, sift together all the dry ingredients.
Using a cheese grater, grate frozen butter over dry ingredients.
Toss gently to incorporate the butter.
Make a well and pour in the cold buttermilk.
Stir until just combined (I use a wooden spoon).
Turn out onto a lightly floured surface.
Knead gently 4-5 times and then pat into a 1-1 1/2" thick rectangle or round.
Cut into rectangles or wedges (this avoids any left over scraps you would get by using a round cutter).
Place close together on parchment paper.
Bake until fluffy and golden brown, about 15-20 minutes.
You can substitute buttermilk with sour milk. Measure 2 tablespoons of lemon juice and add milk to make 1 cup.Please keep in mind that the nutritional information provided below is just a rough estimate and variations can occur depending on the specific ingredients used. *Adapted slightly from Alton Brown