Bring a large pot of water to boil for the pasta.
Add EVOO to a medium saucepan over moderate heat. Add the onions and half of the chopped garlic, and cook until soft, about 5 minutes. Stir in the crushed tomatoes and tomato sauce. Season the sauce with salt and pepper. Let simmer for 8-10 minutes.
While the sauce is simmering, make the meatballs. Place the ground veal and pork in a medium mixing bowl and add the remaining chopped garlic, parsley, egg, bread crumbs, 1/2 cup Parmigiano cheese, salt and pepper. After thoroughly combining everything with your hands, roll the mixture into balls the size of a large walnut and drop into the simmering sauce.
While the meatballs are simmering in the sauce, add the beef bouillon cubes and bay leaf to the boiling water for the pasta. Once the cubes are dissolved, add the spaghetti. Cook to al dente. Right before draining the pasta, reserve a ladle of pasta water for the sauce.
Once the meatballs are cooked through, add the reserved starchy beefy pasta water and the butter to the sauce. Drain the spaghetti, discard the bay leaf and transfer to a large serving bowl. Top with the sauce and the remaining 1/4 cup grated Parmigiano. Pass more grated cheese at the table.