Pre-heat the oven to 375°F.
Add the pork and beef to a bowl and season liberally with salt and pepper. Trim the crust off the bread and chop into fresh breadcrumbs in a food processor; scrape the breadcrumbs into a small bowl and soak in the milk. Return the processor to the base. Squeeze out some of the liquid from the bread and add the moistened bread to the meat; season with a little freshly grated nutmeg, a few grates. Add the beaten egg yolk and half of the chopped parsley to the bowl, a couple of tablespoons. Add two cloves finely chopped garlic to the meat.
Add the mortadella to the food processor and pulse to very finely chop the meat, then add to the ground meats, along with a couple of handfuls of grated Pecorino. Drizzle the meat liberally with EVOO.
Place a baking rack over a baking sheet or cover a baking sheet with parchment paper. Mix the meatballs and roll into large walnut-size balls and roast for 12-15 minutes until light brown, but not cooked through.
Meanwhile, heat the EVOO, three turns of the pot, over medium to medium-high heat in a large Dutch oven. To the warm EVOO, add the fennel seed, chili pepper, onion and sliced garlic; season with salt, pepper and marjoram. Stir for 4-5 minutes, then add the tomato paste and stir for 30 seconds. Pour in the wine and stir for a minute, then add the stock and tomatoes. Break up the tomatoes into small bits. When the sauce comes to a boil, reduce the heat to simmer and add a few leaves of torn basil, reserving a few for garnish. Add the remaining chopped parsley and gently slide in the meatballs. Simmer the mixture for 15-20 minutes to combine the flavors and finish cooking the meat through.
Cook’s Note: Cook the pasta at this time, or if this is a make-ahead meal, cool completely, cover and store. Reheat the sauce, covered, over medium heat until it bubbles, then uncovered at gentle simmer while the pasta cooks.
Cook the pasta in large pot of boiling, salted water to al dente. Save about 1/2 cup of the starchy cooking water just before draining. Add the drained pasta back to the hot pot with the butter, a few ladles of sauce and the reserved starchy liquid. Toss to combine and melt the butter. Serve in bowls with lots of sauce and meatballs on top, lots of shaved cheese and a few leaves of torn basil.
You can add a simple tossed green salad if you like, but it’ll probably get ignored – it is spaghetti and meatballs night!