In a large bowl, combine the first seven ingredients.
Crumble beef and sausage over the mixture and lightly but thoroughly combine. Shape into ½-inch balls.
In a Dutch oven, brown the meatballs in small batches and drain.
Add the broth and pepper and bring to a boil. Reduce the heat and simmer, uncovered, for about 10 minutes. Editor's Tip: Add a couple of splashes of white wine with the broth to produce a fuller-bodied flavor.
Finally, stir in the spinach and cook until wilted, then sprinkle with shredded Parmesan cheese if desired.
