Step #1 First make the sauce: Melt butter In a large-ish saucepan.
Step #2 Remove from heat & stir in the flour, salt & nutmeg until smooth.
Step #3 Gradually add milk & stock or broth; bring to boiling, stirring constantly; boil 2 mins or until slightly thickened.
Step #4 Using a wire whisk beat the egg yolks in a small bowl with the cream.
Step #5 Beat in a little of the hot mixture.
Step #6 Pour back into saucepan; cook over low heat/flame, stirring constantly, until sauce is hot -- do not boil.
Step #7 Remove from heat.
Step #8 Stir in the sherry.
Step #9 Meanwhile, In a large-ish stockpot, bring 6 quarts of water to boiling; add 2 tbsps salt & the spaghetti; cook as label directs; drain in colander.
Step #10 Return spaghetti to kettle.
Step #11 Add 2 c sauce; toss lightly until spaghetti & sauce are well mixd.
Step #12 Combine turkey & mushrooms In a large-ish bowl.
Step #13 Add 2 c of sauce to this mixture & mix well.
Step #14 Divide the spaghetti in half & place this in two 12 x 8 x82-inch baking dishes, arranging around the edges.
Step #15 Spoon half of the turkey mixture into the center of each dish.
Step #16 Reserve rest of sauce for later use.
Step #17 Sprinkle top cheese over spaghetti in each dish.
Step #18 Cover up with foil wrap; put in the fridge 1 hr or overnight.
Step #19 About 1 hr before serrving, preheat your trusty oven to 350 degrees.
Step #20 Bake, covered 45 mins.
Step #21 reheat sauce; spoon over spaghetti in each dish.
Step #22 Note: The above preparation makes a company-attractive casserole.
Step #23 However I usually prefer to mix all the sauce with the spaghetti, turkey & mushrooms in step 3.
Step #24 Another note: To freeze: Line one of the baking dishes with foil wrap; assemble casserole as directed.
Step #25 Fold foil wrap over to seal; freeze right in the dish.
Step #26 When frozen, lift out foil wrap; remove dish from freezer.
Step #27 To serve: Unwrap, return to casserole dish & let this stand 1 hr to thaw.
Step #28 Bake, covered for 1 hr at 350 degrees or until bubbly.
Step #29 One more note; To make turkey stock: Break up carcass.
Step #30 Place in a stock pot with 3 c water, 2 onions (halved), 3 parsley sprigs, 2 carrots (pared & halved) 3 celery tops, 2 tsps salt, 10 black peppercorns, 1 bay leaf.