Preheat oven to 425 degrees.
In the bowl of a food processor combine flour, sugar, baking powder and salt together. Add butter and pulse until the mixture begins to look like cornmeal. Through the feed tube, while the food processor is running, slowing add the milk until dough forms. Be careful not to over mix. If your dough is too soft, add more flour 1 tablespoon at a time.
On a lightly floured surface, roll out the dough until it’s 1/2" thick. Cut with a biscuit cutter. When you cut, lift the cutter straight up and don't twist. You'll get a much better rise on your biscuits.
Butter bottom of a cast iron skillet and place biscuits in pan. Bake until golden brown, about 10-15 minutes.