Barbecued Beef In Crusty Rolls

• 4 french rolls
• 1,000 ml catsup
• 475 gr up beef (cut cooked)
• 10 ml vinegar
• 7 ml worcestershire sauce
• 5 gr onion (finely chopped)
• 5 gr packed brown sugar
• 1 ml dry mustard
• 1 gr pepper
• 4 slices american cheese