In a large bowl, stir together the bread crumbs, parsley, parmesan, egg, garlic, salt, and pepper. Add the ground beef and pork. With your hand in a claw shape, gently incorporate the beef and bread crumb. Shape into about 18 meatballs, about 2 ounces each in size.

In a large pot, heat the olive oil over medium heat. Working in batches, brown the meatballs for 6 to 8 minutes total, rotating them occasionally to brown on all sides. Remove the meatballs from the pot and set aside on a plate.

Remove all but 2 tablespoons of oil from the pot, then add the onion. Cook, stirring occasionally to scrape up brown bits at the bottom of the pan, until the onions are tender, about 5 minutes. Stir in the garlic and red pepper flakes if using, and cook for 1 minute more.

Add the crushed tomatoes, ½ cup water, bay leaf, oregano, salt, and pepper. Stir together and bring the mixture to a simmer over medium heat. Add the meatballs back to the pot (do not stir) and cover. Once the pot returns to a simmer, reduce the heat to low. Simmer gently for 1 hour, stirring every 15 minutes. Stir in the basil.

After 45 minutes of simmering, cook the spaghetti according to package instructions. Reserve about 1 cup of the pasta water, then drain. Toss with 2 cups of sauce and a little bit of pasta water from the pot until the sauce coats the pasta.

Serve the meatballs and sauce over the spaghetti. Top with parmesan cheese and extra basil if desired.