Barbecued Beef with sirloin

1 onion, chopped 1 tablespoon butter 1 tablespoon prepared mustard 1 tablespoon Worcestershire sauce 1 tablespoon distilled white vinegar 2 tablespoons white[...]

1 lb stewing beef , cut into 1 inch cubes. (or 1 lb sirloin steak cut up) 1 medium onion , chopped 4 small mushrooms , sliced 1 tablespoon butter or 1[...]