In a large bowl, whisk together the flour, baking powder, salt, and sugar. Cut the butter into small pieces. Cut in the butter with a pastry blender, until the mixture resembles coarse meal. Gradually stir in 3/4 cup of buttermilk and stir with a fork. Add the remaining buttermilk a teaspoon at a time until dough pulls away from the side of the bowl.
Turn out onto a floured surface, and knead 4-5 times. Pat dough out to 1 inch thick. Cut biscuits with a large cutter (3 inches) or juice glass dipped in flour. Repeat until all dough is used. Brush off the excess flour, and place biscuits onto an ungreased baking sheet.
Bake for 13 to 15 minutes in the preheated oven, or until edges begin to brown.