In a large bowl sift cornmeal, flour, baking soda, salt and allspice.
In a small bowl, combine milk, buttermilk and dark molasses.
Gradually add milk mixture to flour mixture; beat with a spoon just until combined. Stir in raisins. Spoon into coffee cans, filling 2/3 full. Wrap pieces of heavy duty foil tightly over tops.
Place cans on rack in a deep kettle. Add boiling water to kettle to come halfway up sides of cans; cover. Steam 2 1/2 to 3 hours; adding more boiling water as needed. Remove and cool on rack. Serve with baked beans.