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.