Heat the butter in a large pan, add the proscuitto fat or pancetta, carrot, celery and onion and fry gently for 10 minutes.
Add the minced meats and stir with a wooden spoon to break them into smaller chunks. Cook for 15 minutes to brown the meat.
Add the wine and bubble for a few minutes to allow the alcohol to evaporate a little. Stir in a little stock to prevent the mixture from sticking to the pan. Stir in the tomato paste and dilute with a few tablespoons of stock to give a saucelike consistency.
Leave to simmer for 1.5 hours, adding more stock to obtain a smooth consistency.