Soak the bread pieces in cold water for 5 minutes, then mash into a paste with a fork.

In a large bowl, mix the mashed bread with ground beef, sausage, parmesan cheese, garlic, salt, pepper, and the egg until uniformly combined.

Shape the mixture into 1½-inch balls using a scoop or hands. Lightly coat each meatball in flour, tapping off any excess.

Heat oil in a heavy skillet or Dutch oven over medium heat. Working in batches, brown the meatballs on all sides, about 6 minutes per batch. Remove and set aside; they need not be cooked through yet.

In the same skillet, add more oil if necessary, and sauté chopped onion over medium heat until soft and golden, around 5 minutes. Add garlic and cook for 1–2 minutes until aromatic.

Pour in crushed tomatoes and add bay leaves. Bring to a gentle boil, stirring to ensure it simmers uniformly.

Return the browned meatballs to the sauce, partially covering the pot with a lid or splatter screen. Simmer gently for 30 minutes, occasionally turning the meatballs. Five minutes before finishing, stir in basil and adjust seasoning with salt and pepper.

Meanwhile, cook the spaghetti in salted water per package instructions until al dente. Drain and return to the pot.

Combine the cooked pasta with the meatballs and sauce, tossing gently to coat. Serve on a large platter, garnished with parmesan and fresh basil.