An hour (or even a day) ahead, pour the hot water over the dried mushrooms in a small bowl. Let soak to rehydrate at room temperature. When nice and soft, drain them, saving their liquid. Chop up the mushrooms.
Heat a 4 or 5 quart pot on medium heat. Pour in the oil and cook the pancetta or bacon until it begins to crisp. Remove pancetta and save for later. Spoon off excess fat, leaving about 2 tablespoons. If there's not enough fat, add a little oil.
In that fat on medium heat, sauté the onion for 2 minutes, don't allow it to brown. Add the chopped carrots and cook 1 minute. Stir in the tomato paste and cook 5 minutes or so, allowing it to brown, but not burn. Stir it about every minute, giving it time to cook without being disturbed. Stir in garlic.
To the pot, add the ground meat, reserved mushroom liquid, wine, red pepper flakes, black pepper, and nutmeg. Simmer gently about 5-6 minutes. Don't boil.
Stir in the bay leaf, marinara sauce, cream, rehydrated chopped mushrooms and the cooked pancetta or bacon. Simmer gently for 30 minutes, partially covered. Taste and adjust seasoning with salt to your liking.
Meanwhile, near to serving time, cook the pasta in heavily salted water until al dente. Drain. If your sauce still needs to cook a bit longer when your pasta is done, toss your pasta with a little after draining to keep it from sticking together.
Place a cupful of sauce in the bottom of the now-empty pasta pot. Add the cooked pasta and some more sauce. Mix gently. I like to use a light amount of sauce to mix with the pasta and serve the rest of the sauce to be added to plates at the table as desired. Top with Parmesan cheese when serving, as desired.