Barbecue Liver

Ingredients

• 1 pound beef liver
• 1 lg. onion, sliced
• 4 tbsp. butter
• 2 tbsp. vinegar
• 2 tbsp. Worcestershire sauce
• 2 teaspoon sugar
• 2 teaspoon prepared mustard
• 2 tbsp. water
• 3/4 c. ketchup