For the sauce, heat a large Dutch oven over medium heat with oil, 6 slow turns of the pan. Add onions, garlic, salt and pepper, and cook slowly until very soft, 15 minutes, stirring frequently and lowering the heat if the onions begin to brown. Add tomatoes and break them up, add passata, cheese rind and basil, and simmer at a low bubble for a minimum of 30 minutes.
For the meatballs, sauté the onions and garlic in olive oil in a small skillet over medium-low heat until very soft, about 15 minutes. Add a splash of water if the onions begin to brown; let cool.
Soak the bread in milk for 10 minutes then squeeze out excess liquid and crumble into moist crumbs.
Place meats in a bowl and season with salt and pepper. Add breadcrumbs and season with allspice or cloves. Add fennel seeds, red pepper flakes, grated cheeses and eggs to the bowl and mix. Roll large meatballs about 2 ½-inches in diameter and arrange in a baking dish or casserole; drizzle with EVOO. (Tip: The meatballs freeze well but do not add mozzarella if freezing them.)
Bake meatballs at 375 °F for about 15 minutes then cover with about half of the sauce and mozzarella, and bake about 15 minutes more.
Meanwhile, bring a large pot of water to rolling boil, add salt to liberally season water and cook pasta 1-2 minutes less than al dente. Reserve 1 cup of starchy water and drain pasta.
Toss pasta with half the sauce and add starchy water and more grated cheese if you like. Drizzle with EVOO to gloss the sauce and pasta once it emulsifies.
Top with torn basil and serve. Pass meatballs at the table to place on top of pasta.