Place roast in roasting pan; dot with butter and sprinkle barbecue sauce mix over top.
Mix together vinegar, soup and water; pour around meat.
Cover; bake at 325 degrees for 2 hours to 2 hours and 30 minutes, basting occasionally.
When roast is almost done, pour off most of sauce into large pan; return roast to oven.
Bring sauce to boil, adding a small amount of water, if needed.
Sift together flour, cornmeal, baking powder and salt; add milk, salad oil and onion.
Stir until moistened; drop by large spoonfuls into boiling sauce.
Cook 10 minutes; cover and continue cooking for 12 minutes.