DO-AHEAD TIP: Marinate meatballs overnight or for at least 4 hours (see recipe).
In a large bowl, place all ingredients except butter; using your very clean hands, blend thoroughly.
Cover bowl with plastic wrap; refrigerate overnight or for at least 4 hours.
At the time of cooking, form meat mixture into 1- to 2-inch meatballs. Melt the butter in a large skillet over medium-high heat.
Add meatballs and brown for 4 to 7 minutes on each side or until cooked through.