Mix the ground beef, mustard, parsley, eggs, salt, and breadcrumbs to form the meatball mixture. Shape into meatballs, then roll them in flour and set aside.

Meanwhile, heat a pot with oil and chopped onion over medium-low heat. Once the onion is softened, add the meatballs and brown them on all sides, being careful not to burn them.

After browning, add the white wine if available, then add the water to mellow the wine flavor. Cook until a creamy sauce forms. At the end, gently stir the meatballs and cook for another 2 minutes.

Keep the heat low throughout to prevent the flour from burning. The mustard makes the meatballs tender but does not overpower the flavor.