In a small pot, bring dried mushrooms and stock to boil then reduce heat to a low simmer to reconstitute. Remove mushrooms with a slotted spoon, chop and reserve.
Meanwhile, in Dutch oven or heavy pot, heat EVOO, 4 turns of the pan, over medium-high heat. Add pancetta and cook to lightly browned. Add fresh mushrooms and cook to deeply browned, 12-15 minutes. Add carrot, onions, garlic and herbs, and season with salt and pepper. Cook to soften carrots and onions, 8-10 minutes more, then add tomato paste and stir until fragrant. Add wine and deglaze pot, add chopped porcinis and their stock – leaving behind the last few tablespoons of liquid where grit may have settled. Stir in milk and bring sauce to a boil. Reduce heat and simmer to thicken, 45 minutes to an hour.