Cover the dried porcini with boiling water and allow to sit for 15 minutes. Remove the porcini from the water, reserving the liquid, and chop the mushrooms fine. Heat a wide heavy-bottomed pan; pour in 2 tablespoons of olive oil and add the diced pancetta. After the pancetta has released some fat, add the onion, celery, carrot, and a little salt. When the vegetables have softened somewhat, add the garlic and porcini, and cook until the vegetables are soft. Remove the vegetables from the pan and set aside.

Put the pan back on the heat (you don’t need to wash it), pour in 2 more tablespoons of oil, and when it is hot, add the skirt steak, pork, and a little salt. Cook over medium-high heat until the meat begins to brown, about 15 minutes. Turn the heat to medium and add the cooked vegetables, wine, bay, and thyme. Adjust the heat to maintain a low simmer and let the sauce cook until the liquid evaporates and the contents begin to brown. Deglaze with 1 cup of the stock and a few tablespoons of the milk; add the tomato paste, making sure to scrape the brown bits off the bottom of the pan and stirring the sauce well to incorporate the milk. Continue to cook the sauce gently, adding a few tablespoons of milk and stock now and then. Reduce the sauce until the liquid evaporates and everything begins to brown again; this gives the sauce depth and color. Deglaze with the rest of the stock and milk, stirring and scraping well. Skim the fat that rises to the surface of the sauce. The sauce is done when its texture is velvety and the meat is completely tender, in about 1½ hours. Cool and refrigerate for up to 4 or 5 days.

Reheat and serve over pasta, garnished with the chopped parsley, and pass Parmesan cheese and the pepper mill.

Variation: This basic recipe can be used with other kinds of meat and even poultry—guinea hen is especially good. Another variation worth trying is to add sautéed fresh wild mushrooms at the end of the cooking.