Place the mushrooms in a small saucepan and cover with the stock or water. Bring to a boil, then lower the heat and simmer on very low heat to reconstitute (or pour 1 cup boiling water over them, cover and let stand for 10 minutes).
Bring a large pot of water to a boil, salt it, add the pasta and cook until al dente. Drain, reserving 1 cup of the starchy cooking water.
While the pasta is working, in a heavy pot, heat the EVOO, two turns of the pan, over high heat until smoking. Stir in the veal to brown slightly, then stir in the sausage, crumbling the meat as it cooks. Add the carrot, celery, onion, garlic and sage; season generously with salt and pepper. Cover and cook the vegetables, stirring occasionally, until softened, 3-5 minutes. Stir in the tomato paste, then stir in the wine to deglaze, scraping up the browned bits from the bottom of the pan.
Remove the mushrooms from their soaking liquid and chop. Stir the mushrooms into the ragu with their strained liquid, leaving any sediment behind. Stir in the milk, lower the heat to medium-high and cook to thicken.
Stir the reserved 1 cup of starchy cooking water into the ragu. Add the pasta and toss to coat. Top with a liberal amount of cheese.