Barbecue Sauce

1/3 c. vinegar
2/3 c. water
1 1/2 T. prepared mustard
1/3 c. brown sugar
1/4 tsp. pepper
1 tsp. salt
1 1/2 T. Worcestershire sauce
Pinch cayenne pepper
2 lemon slices
1 large onion, sliced
1/2 c. butter or margarine

Combine all ingredients. Simmer, uncovered for 20 minutes.