In a large bowl combine the beef, pork, parmesan cheese, egg, milk, breadcrumbs, garlic, salt, pepper, parsley, oregano and Calabrian chili paste (if using).
Mix well and form into balls (I use a 3 Tbsp scoop to make around 20 meatballs).
Set a large, heavy skillet over medium heat and coat the bottom with oil, about 2 Tbsp. Once the oil is hot, add the meatballs to the skillet in batches and turn often until all sides are browned.
Remove any excess oil from the pan, if necessary.
Pour the marinara sauce over the meatballs.
Evenly spread the cheese over top of the meatballs.
Bake at 400 degrees for 20-30 minutes, until the meatballs are cooked through, the sauce is bubbling and the cheese is melted.
Serve with fresh parsley or basil, red pepper flakes and crusty bread for mopping up extra sauce.