Combine ground meats, bread crumbs, eggs, cheese, chile flakes, salt and stock mixture in a large bowl and mix lightly with hands until uniform. Do not overmix.

Rub hands with a little olive oil and form mixture into 2-oz. balls.

Heat oil (about 1/2-inch deep) over medium-high heat in a large skillet. Brown meatballs, turning once. Do not crowd meatballs. Drain; simmer in marinara sauce. Serve over spaghetti if desired.