Sift together into a bowl the flour, sugar, baking powder, salt, and cream of tartar.
Add the butter or margarine. With a fork or a pastry blender cut the butter in util the mixture resembles coarse meal. Stir in the milk and the egg, just until combined. Turn the dough onto a floured board and knead lightly 4 or 5 strokes. Roll or pat (being careful to handle the dough as little as necessary) into a 1/2-3/4-inch thick round. Cut with a biscuit cutter and place on an ungreased baking sheet, farther apart if you like crispy edges, and closer together if you like them soft.
Bake at 425F for 10-15 minutes. (For elevations of 500 feet or more use 4 teaspoons of baking powder.).