Preheat oven to 375 degrees F. Combine beef, onions, garlic, eggs, cheese, seasoning, salt and pepper in a large bowl. Blend chopped mushrooms into meat mixture. Slowly add the broth or marinara sauce, 1/2 cup at a time. The mixture should be very moist but still hold its shape if rolled into meatballs. Shape into meatballs. Arrange in a single layer on a large, shallow baking sheet. Bake meatballs in the preheated oven 35 minutes, turning occasionally, until evenly browned.

My suggestion is to only serve the sauce on the noodles you will eat that night. The leftover noodles and sauce get a little soggy, so reserve both separate.