Rinse the spinach well, discard the roots, and heat it in a pot until it wilts, then squeeze out the excess moisture, chop it coarsely, and sautÃ© in 2 tablespoons butter.
Mince the remaining herbs (carrot, onion etc.) and brown them lightly in 2 tablespoons butter.
When they have browned add the pork and continue cooking until it is browned too, then stir in the soaked mushrooms. Stir in the Marsala and the diluted tomato paste, season to taste with salt, pepper and nutmeg, reduce the heat to a low simmer, and simmer for an hour, adding more water if necessary to keep the sauce from thickening overmuch.
While the sauce is simmering roll out the dough if you're starting from scratch, and cut it into 3 by 4-inch rectangles. Once the pasta is cut cook it a few pieces at a time in abundant lightly salted water (if you're using commercially prepared shells follow the directions on the package). Remove the pasta from the water with a slotted spoon while it's still rather al dente, and lay the pieces on a damp cloth taking care lest they be touching and stick.
When the sauce is done, remove the pot from the fire and transfer the meat and mushrooms to a bowl, leaving the sauce in the pan. Crack the remaining egg into the bowl, add the chopped spinach and the grated cheese, a hint of nutmeg, 2 tablespoons of the sauce in the pan, and mix thoroughly.
Preheat your oven to 350 F (175 C).
You are now ready to fill your cannelloni: lay some of the filling along the long edge of the first sheet, roll it up to make the cannelloni, and place it in a well buttered, elegant baking dish. Repeat the procedure until pasta and filling are all used up.
When you are done making the cannelloni, spoon the remaining sauce from the pan over them, together with a little water, dust them well with grated cheese and dot them with a little butter, and bake them for about a half hour, which will give the flavors time to meld.