In a large saucepan, saute onion and olive oil together for a few minutes. Add the remaining ingredients into pot and simmer.
Meatballs
Crumble white bread, Parmigiano-Reggiano cheese, parsley, salt, pepper, and minced garlic together in a large bowl.
Next combine ground beef, milk, and egg into the cheese mixture. Mash with hands to combine completely. Form 1 inch meatballs with hands and set aside until all are done.
Preheat oven to 350 °F and prepare a skillet that can go into the oven. Brown meatballs on medium high heat on one side and then flip balls over to brown the other side.
Place skillet of meatballs in the oven and bake for 30 minutes.
Remaining Entree
Bring a large stockpot of water to a rolling boil and add spaghetti pasta. When done, drain pasta, top with baked meatballs, and spaghetti sauce. Sprinkle with some more grated cheese and enjoy.