Sauté mushrooms in butter until browned. Prepare spaghetti according to package directions, using salted water. Make a cream sauce by blending butter and flour and gradually adding hot broth. When this mixture reaches boiling point, reduce heat and add the cream, sherry, salt, and pepper to taste. Divide the sauce in half. Add the turkey and mushrooms to ½ the sauce, the spaghetti to the other half. Place the spaghetti mixture in a ring in a well greased casserole. Place the turkey and mushroom mixture in the center. Cover with cheese. Bake, uncovered, at 325F until browned and bubbly.