Combine first 5 ingredients in a large bowl; cut in shortening with a pastry blender until mixture is crumbly. Add buttermilk, stirring until dry ingredients are moistened. Turn dough out onto a lightly floured surface, and knead lightly 4 or 5 times.
Roll dough to 1/2-inch thickness, cut with a 2 1/2-inch round cutter, and place on lightly greased baking sheets. Brush biscuits with egg. Bake at 425° for 10 minutes or until golden.