Grease baking dish and add speghetti noodles. Preheat oven to 350F. Melt half the butter in a large sauce pan over medium heat and cook the mushrooms, stirring, until they are softened. Transfer to baking dish.
In the saucepan, melt the remaining butter over medium heat, and the flour and cook, stirring, for 2 minutes. Stir in the chicken broth, cream and sherry. Bring the sauce to a boil, stirring, and simmer for 5 minutes. Remove from heat and add the turkey. Season with nutmeg, salt and pepper.
Stir the sauce into the baking dish with the mushrooms and spaghetti, mixing a little. Sprinkle with parmesan and bake in the middle of the oven at 350F for 25 to 30 minutes until cheese is golden brown.