Heat in a large heavy-bottomed pot:
1 tablespoon olive oil
Add:
2 ounces pancetta, diced fine
Cook over medium heat until lightly browned, about 5 minutes. Add:
1 small onion, diced fine
1 celery stalk, diced fine
1 carrot, diced fine
2 garlic cloves, finely chopped
5 sage leaves
2 thyme sprigs
1 bay leaf
Cook over medium heat, stirring occasionally, until tender, about 12 minutes
While the vegetables are cooking, heat in a large heavy-bottomed pan, preferably cast iron:
1 tablespoon olive oil
Add and brown over medium-high heat, in two batches:
1 pound skirt steak, cut into 1/8-inch cubes
4 ounces pork,ground
Cook until the meat is a nice chestnut color. Once all the meat is browned, pour in:
1 cup dry white wine
Reduce the wine by half, scraping the brown bits off the bottom of the pan. Add the browned meat and the deglazing juices to the tender vegetables with:
2 tablespoons tomato paste
Salt
Measure and stir together:
2 cups beef or chicken broth
1 1/2 cups milk
Pour enough of this liquid into the pot to bring it to the level of the meat and vegetables. Simmer gently until the meat is very tender, about 1 1/2 hours. As the liquid reduces, keep topping it up with the rest of the broth and milk, and skimming the fat that rises to the surface.
When the meat is tender, remove the sauce from the heat and season to taste with more salt, if needed, and:
Fresh-ground black pepper
Variations:
Include 1/4 cup dried porcini, soaked, drained, and chopped fine, with the diced vegetables.
Other cuts of beef can be used instead of skirt steak. Chuck or hanging tenderloin will make a delicious sauce, although hanging tenderloin will require at least an hour more of cooking time to become tender. During the additional cooking time it may be necessary to add more broth or milk to keep the sauce from becoming too dry.