In a dutch oven, combine the chicken with enough salted water to cover it by 5 cm, bring the water to a boil, and simmer the chicken for 20 minutes, or until it is tender. Let the chicken cool in the broth, separate the meat from the skin and bones, returning the skin and bones to the broth, and cut the meat into strips, reserving it. Simmer the broth until it is reduced by half, strain it through a fine sieve, discarding the solids and skimming the fat, and boil it until it is reduced to about 2 cups.
While the broth is reducing, in a large saucepan cook the mushrooms in 2 tablespoons of the butter over moderately low heat, stirring, until they are softened. In a kettle of boiling salted water boil the spaghetti until it is al dente and drain it well. In a saucepan melt the remaining 3 tablespoons butter over moderately low heat, add the flour, and cook the roux, stirring, 3 minutes. Whisk in the reduced broth, the cream, and the Sherry, bring the sauce to a boil, whisking, and simmer it for 5 minutes. Season the sauce with the nutmeg and salt and pepper. Stir half the sauce into the mushrooms with the spaghetti and transfer the mixture to a well-buttered 2.5-quart baking dish, making a well in the center. Add the reserved chicken to the remaining sauce, combine the mixture well, and transfer it to the center of the spaghetti mixture. Sprinkle the mixture with the Parmesan and bake it in the middle of a preheated 350 deg. F. oven for 25 to 30 minutes, or until it is pale golden.
Busted By: Barbra <barbra@theofice.net>