This is based very closely on Marcella Hazan's recipe in Marcella Says...
I don't think the exact proportions of the different varieties of mushrooms are essential; however, you do want both dried and fresh, as the dried provide an earthy richness that makes the dish much more interesting.
1 oz dried porcini mushrooms
1 oz dried shiitake mushrooms
2-4 oz sundried tomatoes, roughly chopped
8 oz fresh shiitake mushrooms
8-12 oz fresh cremini mushrooms
8-12 oz fresh white button mushrooms
1 c finely chopped shallots
4 T butter
1 c finely chopped onion
1-1 1/2 lbs ground veal
1 c dry white wine
1/4 c dry vermouth
6-10 fresh ripe plum tomatoes, peeled, seeded, chopped
freshly ground black pepper
The day before, put the dried porcini and shiitake mushrooms in a heat safe container (I use a 3-cup glass measuring pitcher) and pour very hot or boiling water over them. Let soak overnight. Do the same for the tomatoes if they are very dehydrated. If not, maybe soak for an hour or two before preparing.
When ready to prepare, remove and discard the fresh shiitake stems. Brush mushrooms with a damp cloth as needed to clean them, then slice very thin.
Strain dried mushrooms, pouring liquid into a bowl to set aside. Wash the soaked mushrooms, and cut any oversized pieces into bite-sized ones. Pour the soaking liquid through a coffee filter or paper towel to remove grit and dirt.
Heat the olive oil over medium high in a 12" saute pan, and add the shallots. Cook, stirring occasionally, until colored a deep gold. Add the soaked mushrooms, cook for a minute or two, then add the soaking liquid and cook until liquid has evaporated.
Once liquid is gone, add as many of the fresh mushrooms as will fit, and sprinkle with salt. Turn them over once or twice to coat well, then turn the heat down to medium/medium-low. When the mushrooms have released some liquid and shrunk in bulk, add the remaining mushrooms. Cook, turning over occasionally, until they are very soft and all liquid has evaporated; this will probably take about 90 minutes. Remove from heat.
Meanwhile, when mushrooms are cooking, put the butter and the chopped onion in a second saute pan. Cook the onion, stirring from time to time, until it begins to brown. Add the ground veal, crumbling it with your fingers or a fork, and turn to coat well. When the meat has browned lightly and uniformly, pour the wine and vermouth into the pan, and add salt/pepper to taste.
Once the wine has bubbled away completely, add the sundried tomatoes and fresh tomatoes, and turn the heat down to the lowest setting possible (on your smallest burner). Cook uncovered for about 45 minutes, stirring from time to time.
Once both meat and mushrooms are finished, empty contents of both pants into a large bowl, and stir gently but thoroughly to combine.
Wipe both pans clean. Divide the meat-mushroom mixture between both pans, and cook on medium low for about 20 minutes, stirring frequently. If not using the sauce the same day, empty the contents of both pans into the bowl, cover and refrigerate. Reheat gently but thoroughly before using.
You can refrigerate the finished sauce in a tightly sealed container for 5 days, or you can freeze it for up to 3 months. Bring to room temp before reheating.