The Best Baked Beans

2 cans pork and beans, drained
1 cup ketchup
1 small onion, diced
1 tablespoon yellow mustard
1 cup brown sugar
3 slices bacon, cut into 2-inch pieces
In a large bowl, combine the first five ingredients. Place in a buttered 13x9 casserole dish and top with bacon pieces. Bake at 300 degrees for 2 hours.