To make the meatballs, add the bread and rosemary or thyme into a food processor and blitz until it turns into breadcrumbs. Tip into a large bowl and add the mince, liver and collagen (if using), cumin, oregano, garlic and egg yolk. Season well with a few pinches of salt and pepper. Mix well with a wooden spoon, then with wet hands, roll meatballs into approximately 1 tablespoon-sized balls.
Place a heavy-bottomed casserole pot or oven-proof frying pan over medium heat with the olive oil or ghee. Add the meatballs, and cook for 5 minutes, tossing regularly, until browned all over. Transfer meatballs to a plate with any of the pan juices.
To make the Simple Sauce: place the casserole pot or frying pan back over the cooktop and reduce to a low heat and add the olive oil or ghee. Add the garlic and oregano, stirring frequently until golden and fragrant. Add the tomatoes and Bone Broth or water. Increase heat to medium-high heat and bring to the boil. Reduce heat to low and gently simmer for 45 minutes, but if you’re in a rush, it can be ready in 10 minutes!
While the sauce is simmering, preheat the oven to 180°C fan-forced.
Once the sauce has reduced to your liking, add the vinegar, basil leaves and season well with salt and pepper.
Add the reserved meatballs and resting juices back into the pan with the sauce. Top with the reserved basil leaves, and press the slices of fresh mozzarella just into the sauce. Grate over the Parmesan cheese and drizzle the top with olive oil. Place into the oven and bake for 15 - 20 minutes, until the cheese is golden and melted and the sauce is bubbling.
Serve the meatballs on top of cooked pasta, sourdough or with some Mashed Cauliflower.