Soak the white bread in cold water for 5 minutes, then mash it with a fork until smooth.
In a large bowl, combine the soaked bread, ground beef, sausage, Parmesan cheese, minced garlic, sea salt, black pepper, and the egg until fully mixed.
Shape the mixture into 1.5-inch meatballs, roll them in flour, and set them aside.
Heat the olive oil in a large skillet over medium heat.
Add the meatballs in batches, browning them for about 6 minutes.
In the same skillet, sauté the chopped onion until soft, about 5 minutes.
Add the minced garlic and cook for another minute, stirring frequently.
Stir in the crushed tomatoes and bay leaves, bringing the mixture to a gentle boil.
Add the browned meatballs to the sauce, reduce the heat to low and let it simmer for 30 minutes.
In a large pot, boil salted water and cook the spaghetti until it reaches al dente, according to package instructions.
Drain the spaghetti and return it to the pot. Pour the sauce and meatballs over the pasta, tossing gently to coat.
Serve each plate garnished with additional Parmesan cheese and minced basil.