In a large mixing bowl, measure out your flour and add the sugar if you choose to.
Quickly grate the butter into the bowl of flour. Alternatively, you can cut the butter into the flour with a pastry blender until the mixture resembles coarse crumbs, which takes about five minutes to achieve. If there is any wait time between this step and the next, store your dough in the fridge until you are ready.
Make a well in the center of the mixing bowl and add the buttermilk or milk. Stir the liquid in gently until it barely comes together with the flour. Be careful NOT TO OVERMIX the dough.
Let it rest in the fridge for about 10 minutes while you prepare a lightly floured surface like a clean countertop or a cutting board for the next step.
Transfer the biscuit dough to your floured surface and knead it 3-4 times. Don't overdo it - you should still see flakes of butter throughout the dough.
Very gently pat the dough out with your hands or use a rolling pin to spread the dough evenly until it is about ½ inch thick.
Fold the dough over itself 6-8 times to achieve those flaky layers. After folding, press the dough down with your hands until it is about 1 inch thick.
Use a 2-3-inch round cookie cutter or the rim of a glass to cut out the biscuits. Firmly push straight down and then pull straight up. Use your hands to loosen the dough from the cutter and transfer it to a baking sheet. Spread the biscuits out evenly across the baking sheet.
Knead bits of leftover dough back together and repeat until the dough is used up. Your last few biscuits may not look as pretty as the first ones, but don't worry, they'll taste just as good.
Lightly brush each biscuit with buttermilk or biscuit dough.
Bake at 400℉/205℃ for 12-15 minutes until they are lightly browned.