Aunt Patty'S Bean Casserole - cooking recipe

Ingredients

1/2 stick butter or margarine
1/2 c. chopped onion
1 Tbsp. white vinegar
1/2 tsp. light mustard
1/2 c. brown sugar
1/2 c. ketchup
1 can kidney beans *
1 can butter beans *
1 can baked beans *
canned or fresh mushrooms to taste (about 1/2 lb. fresh)

Preparation

*Can use larger than 16-ounce size if you like.