Calico Beans

I made these again for the first time in a few years for a picnic last night.  I had forgotten how tasty they were/are!

1 lb. ground beef
1 onion, diced
3 small cans pork and beans
2 small cans kidney beans, drained and rinsed
1 small can butter beans or cannellini beans (pretty much any white bean can be used), drained and rinsed
1 c. brown sugar
1 c. ketchup
2 Tbl. vinegar
2 tsp. mustard
2 tsp. salt

Cook beef and onion over medium heat until no pink remains;  drain.  Combine with the rest of the ingredients and place in a 9x13 dish.  Cover and bake at 350 for 30 minutes.  Remove cover and bake for an additional 15 minutes.