Preheat oven to 375 degrees F.

Combine the meat with the mushrooms and the remaining meatball ingredients. Mix well with your hands until thoroughly combined. Form about 15 balls, place on a rimmed baking sheet, and bake for 25 minutes, until the internal temperature reaches 160 degrees (or until the juices run clear).

While the meatballs are baking, sauté the mushrooms in the fat for about 5 minutes.  Add the remaining sauce ingredients and cook for about ten more minutes.