Bring a large pan of salted water to the boil and put in the cannelloni.
Stir for a minute so that it does not stick together.
Cookfor about 10 minutes until just tender.
Drain well and leave to cool while preparing the filling.
Chop the onion and garlic finely .
Chop the mushrooms coarsely .
Heat the oil in a pan and cook the onion, garlic and mushrooms for 5 minutes over low heat, stirring well.
Cut the chicken into pieces and chop very finely .
Discard the crusts, and make the bread into crumbs .
Grate the cheese .
Stir the chicken into the onion mixture with the bread crumbs, cheese and marjoram.
Remove from the heat and work in the egg, salt and pepper.
Cool and then divide the filling between the pieces of pasta.
Roll up lengthwise.
Arrange the pasta in a buttered ovenproof dish.To make the sauce, mix 3 tablespoons butter, the flour and milk until smooth .
Pour into a pan, bring to a boil and simmer for 3 minutes, stirring all the time.
Stir in the cream and heat gently, stirring well.
Season with salt, pepper and nutmeg.
Spoon the sauce over the pasta and dot with flakes of the remaining butter.
Grate the cheese and sprinkle it over the pasta.
Bake at 375°F for 30 minutes.
Serve as a first course, or as a main course with green salad and crusty bread.