Preheat oven to 400 °F.
Prepare the meatballs: Put all ingredients into a large mixing bowl. Knead everything together with clean hands. You want to feel for the right texture. It should be soft, but not sopping wet. If it's not soft enough, add 1 more tablespoon of milk.
Once all ingredients are combined, form balls the size of an egg by pushing them into the shape softly in your hands. Do NOT roll the meat into balls on your palms! Baby the meat, form it lovingly into the balls.
Place meatballs on a nonstick baking sheet. Bake for 30 minutes, remove and reserve.
Prepare the sauce: Heat oil in a large saucepan over medium heat. Add the garlic and onion, and sprinkle the salt over them to bring out their flavor. Break pepper in half to release the seeds and add it to the pot. Cook, stirring occasionally, until the onion is translucent, about 5 minutes.
Add the can of crushed tomatoes. Bring to a boil. Add parsley. Reduce the heat to medium-low. Simmer, stirring occasionally, for 5 minutes.
Carefully add the meatballs to the pan. Simmer, stirring occasionally, for 30 minutes.
Serve meatballs and sauce over spaghetti.