Combine flour, baking powder, and sugar; stir well. Cut in shortening until mixture resembles coarse meal. Gradually add buttermilk, stirring until dry ingredients are moistened.
Turn dough out onto a lightly floured surface, and knead 10 to 12 times.
Roll dough to 1/2-inch thickness; cut with a 3 1/4-inch biscuit cutter. Place biscuits on a greased baking sheet; brush with butter. Bake at 450° for 12 minutes or until lightly browned.