In a large mixing bowl, combine the cooked chicken, sour cream, uncooked spaghetti, cream of chicken soup, drained mushrooms, melted margarine or butter, and white pepper.
Mix well.
Assemble Casserole:
Transfer the mixture into a greased 13 x 9-inch casserole dish, spreading it evenly.
Cover and refrigerate for at least a half a day to allow the pasta to absorb the liquid.
Preheat Oven:
When ready to bake, preheat your oven to 350°F (175°C).
Bake:
Sprinkle the freshly grated Parmesan cheese evenly over the top of the casserole.
Bake in the preheated oven for 25-30 minutes or until the casserole is bubbly and the cheese is melted and golden brown.
Freezing Option:
If you choose to freeze the casserole, cover it tightly with aluminum foil before freezing.
When ready to bake, thaw it in the refrigerator overnight, then bake as directed.
Notes / Tips / Wine Advice:
Wine Pairing:
A Pinot Grigio or a light Chardonnay would pair well with this creamy and savory casserole, balancing its richness with a refreshing acidity.