Combine first 3 ingredients in a large bowl; cut in shortening with pastry blender until mixture is crumbly.
Add buttermilk, stirring with a fork until dry ingredients are moistened. (Dough will resemble cottage cheese and be sticky.)
Turn dough out onto a heavily floured surface, and knead lightly 4 or 5 times.
Roll dough to 3/4-inch thickness; cut with a 2 1/2-inch round cutter. Stack two baking sheets, one on top of the other. Lightly grease top baking sheet.
Place biscuits on top baking sheet, and bake at 450 for 10 to 12 minutes or until lightly browned.