Prepare the Tomato Sauce:

In a large skillet, heat olive oil over medium heat. Add the chopped onion, carrots, celery, and parsley. Stir to coat the vegetables in the oil, then reduce the heat to low and cover the skillet. Cook the mixture for 15 to 20 minutes, or until the vegetables are tender. Once softened, remove the lid and add the minced garlic, cooking for an additional 30 seconds. Add the tomatoes to the skillet, breaking them up if using whole canned tomatoes. Stir in the basil and tomato paste, then season with salt and pepper. Allow the sauce to simmer over low heat, uncovered, for 15 to 30 minutes, until it thickens. For a smoother texture, purée the sauce in a blender or pass it through a food mill before returning it to the skillet to adjust the seasonings.

Prepare the Meatball Mixture:

Heat the milk in a small pot until it is steamy, then remove from heat. Tear the bread into small pieces and soak it in the milk until it partially dissolves, then mash it to form a paste. Set the mixture aside to cool. In a large bowl, combine the ground beef, ground pork, ricotta cheese, grated Parmesan, eggs, garlic, parsley, oregano, salt, and pepper. Add the cooled bread-milk mixture and gently mix everything together with your hands. Be careful not to overwork the mixture, as this will result in dense meatballs. Some small pieces of bread and meat are acceptable.

Form the Meatballs:

Wet your hands to help form the meatballs. Each meatball should be approximately 2 to 3 inches in diameter, but you may adjust the size as desired. Roll the formed meatballs in flour to coat them evenly. Place them on a baking sheet as you proceed. Rinse your hands periodically during this process to keep things tidy.

Brown the Meatballs:

Heat the olive oil in a large skillet over medium-high heat. Once hot, add the meatballs and brown them on at least two sides. Since the meatballs will cook further in the sauce, they don’t need to be fully cooked through at this stage.

Simmer the Meatballs in Tomato Sauce:

Once the meatballs have been browned, gently add them to the simmering tomato sauce. Turn each meatball in the sauce to ensure they are coated. Cover the skillet and allow the meatballs to simmer in the sauce for 15 to 20 minutes, ensuring they are fully cooked through. Serve with the sauce, either alongside pasta or crusty bread. Optionally, garnish with freshly chopped parsley.