Mix flour, salt, baking powder, and shortening with a pastry blender (if you don't have one, you can use two knives, but it is TONS easier with the pastry blender) until texture is crumb-like.

Combine egg, vinegar, and water and then add to flour mixture. Mix well with a fork.

Shape dough into a ball and wrap in plastic wrap and aluminum foil. Chill well; at least two hours before rolling out.