Preheat oven to 425 degrees (225 C.).

In a large bowl, sift together flour, baking powder, salt and baking soda.

Using a pastry blender or two 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 on a lightly floured surface.

Gather into a disk.

Knead lightly a few times just until smooth.

Pat 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-in. thick, and cut out more biscuits.

Bake the biscuits until golden, 12 to 15 minutes.

Serve hot.