I don’t have a recipe, but use a combination of ground pork and beef. If I can find it, sometimes stores will carry a "meatloaf mixture" – ground pork, veal, and beef. I add finely chopped onion, garlic, and celery, Parmesan cheese, salt and pepper.
Something I got from Cook’s Illustrated – for every pound of meat mixture – use two slices of white bread – remove crusts,tear in small pieces, make a paste mashing into 1/3 cup buttermilk. Mix well, shape the meatballs, bake in oven until browned, remove, drain, before adding to the sauce.