Mix dry ingredients and stir in molasses and sour milk. (To make sour milk, add 1 T Vinegar to 1 cup sweet milk). Grease two #2 tin cans and place rings of waxed paper in bottoms. Divide batter evenly between the two cans, and cover with aluminum foil. Place in covered kettle of boiling water, bring water half way up sides of cans, and boil for two hours. When ready to serve, unmold by running knife around inside of can and shaking out onto plate. Cut thinly and serve with Boston Baked Beans.