How to Make It
In a large measuring cup, soak the porcini in the hot water until softened, 15 minutes. Using a slotted spoon, scoop out the mushrooms and squeeze the liquid back into the cup. Chop the mushrooms.
Meanwhile, in a large enameled cast-iron casserole, heat 2 tablespoons of the oil. Add the onion, carrots and celery and cook over moderate heat, stirring until softened, 6 minutes; spoon onto a plate.
Add the remaining 2 tablespoons of oil to the casserole. Season the veal with salt and pepper and dust with flour. Add the meat and bones to the casserole and cook over moderately high heat, turning once, until browned, 10 minutes. Add the wine and cook, scraping up any bits, until nearly evaporated, about 5 minutes.
Return the vegetables to the casserole. Add the tomatoes, marjoram sprig and porcini. Slowly pour in 2 cups of the porcini liquid, stopping when you reach the grit. Season with salt and pepper and bring to a boil. Cover and simmer over very low heat until the meat is very tender, 2 hours. Scoop the marrow from the bones and stir it into the ragù. Discard the bones and marjoram sprig and stir in the chopped marjoram.
In a large pot of boiling salted water, cook the pasta until al dente. Add the pasta to the ragù and toss gently. Serve in deep bowls, passing the cheese on the side.