In a large mixing bowl combine the tomato soup, brown sugar, apple cider vinegar, and Dijon mustard with a whisk and set aside.
To another large mixing bowl combine the meats, eggs, graham cracker crumbs, onion, milk, and salt. Mix well.
Use a 3 Tablespoon scoop to portion out meat approximately the size to fit in the palm of your hand. Shape into 15 balls and set 3 rows of 5 snuggly into a 9x13 casserole dish.
Pour the sauce over all the ham balls, covering completely.
Bake in the oven for 1 hour uncovered, basting half way through.
Garnish with parsley if desired.
Notes
These ham balls are really are quite large. That's the "thing" about them, aside from being sweet. You can make them smaller but not less than ¼ cup. It's a wet mixture, so to stay together, the balls do need to be bigger than the average meatball.