Begin by finely chopping the onion, celery, and carrot. You can use a food processor for a finer texture, which also helps incorporate more vegetables into the sauce.
In a pan, heat a combination of butter and olive oil over medium heat. Add the chopped onion, celery, and carrot, and sauté until they become soft.
Next, add the meat to the pan and cook it until it is browned.
Once the meat is browned, incorporate the jarred tomatoes. If using whole San Marzano tomatoes, you can blend them in a food processor for a smoother consistency.
Pour in the chicken stock and sprinkle in the nutmeg, salt, and pepper. Stir everything together.
Allow the sauce to simmer for a few minutes, letting the flavors meld together before serving.
