This is the first recipe I found. I have tried some easier recipes but this is still my favorite. It makes two 8" x 12" pans which is fine if you have that much turkey - but it is a lot. You can freeze it before baking - if you make the full recipe - which is a good option. Below is the recipe, halved.
LINK to the original recipe which is from McCall's Cooking School. It includes the instructions for how to freeze before baking - and then how to bake from frozen.
HALF RECIPE - one 8" x 12" pan - makes 6 generous portions ( 8 portions - if there were side dishes)
Make a white sauce with
6 tablespoons butter and 6 tablespoons flour
1 1/2 tsp salt
1/16 tsp nutmeg
2 cups milk and 1 cup broth (chicken or turkey
After boiling the sauce gently for 2 minutes
whisk together 2 egg yolks and 1/2 cup heavy cream
Temper the egg mixture, return to the sauce pan and bring up to heat, but not boiling
Stir in 1/4 c dry sherry
While you are working on the sauce, boil 1/2 lb spaghetti in salted water until al dente.
Drain 1 can of mushroom pieces (or saute fresh mushrooms) OPTIONAL - saute some onion, celergy and a little garlic. It's not in the original recipe - but - it's a very nice addition - mince everything so that the flavors are in the white sauce - but it's not chunky.
Combine 3-4 cups turkey with mushrooms, cooked spaghetti, and 2 cups (or a little more) sauce.
Pour into a greased casserole - and top with 4 oz or 1 cup grated sharp cheddar cheese. Add Parmesan if you with, not in original recipe.
Preheat over to 350 to bake. Bake, covered, for 45 minutes - or until bubbly - let it rest before serving.
Reheat the leftover sauce to serve over the top of each serving.