Place the flour, sugar, baking powder, butter and shortening in a bowl. With the tips of the fingers gently rub the fat into the dry ingredients until the mixture resembles coarse oatmeal.
Beat the egg with the water and add with the vanilla to the flour mixture. Blend the dough into a ball with a fork or the fingers. Wrap in wax paper and chill for several hours, until firm. The dough can be kept for several days in the refrigerator, or it may be frozen.