Use a canning kettle, and invert the wire rack. Fill with water to just below the wire rack. Bring to a boil on top of the stove.
In a large bowl, mix together molasses, oil, milk, sugar, salt, and baking soda. Stir in white and graham flour. Divide batter into two 1 pound coffee cans. Place a double thickness of aluminum foil over top, and secure with rubber bands.
Keep water at a slow boil, and steam for one hour.