Preheat the oven to 425 F. In a large bowl, sift together flour, baking powder, salt, and baking soda. Using a pastry blender or 2 knives, cut the shortening into the flour mixture until coarse crumbs form. Add the buttermilk, tossing with a fork until a dough forms. Turn dough out onto a lightly floured surface. Gather into a disk. Knead lightly a few times just until smooth. (The dough can be made up to 2 hours ahead, wrapped in plastic wrap, and refrigerated until ready to use.) Pat the dough to 3/4-inch thick. Using a biscuit cutter or a glass dipped in flour, cut out biscuits. Place the biscuits, 2 inches apart, on an ungreased baking sheet. Gather dough trimmings, pat to 3/4-inch thick, and cut out more biscuits. Bake the biscuits until golden, 12 to 15 minutes. Serve hot.

Baking Tip: To produce flaky biscuits, take care not to overhandle the dough. For less waste and a speedier preparation, pat the dough into a square, then cut into square-shape biscuits with a floured knife. Bake as directed above.

American Home Baking series.