If desired, substitute two 10¾-ounce cans condensed cream of mushroom or chicken soup mixed with ½ cup milk and ½ cup chicken broth for the butter/mushroom/flour/chicken broth/milk mixture. If you are using leftover pasta, you will need about 4 cups. Cooked chicken may be substituted for the turkey.
Preheat the oven to 400°F. Grease a 13 × 9-inch baking dish.
Cook in a large pot of boiling salted water:
Meanwhile, melt in a saucepan over medium heat:
Add and cook, stirring, until softened, about 5 minutes:
Stir in until well blended:
Slowly add while whisking:
Bring to a boil, reduce the heat, and cook until the sauce is thickened and smooth, about 5 minutes. Mix in:
Drain the pasta and gently mix into the turkey mixture. Pour into the prepared dish. Mix together in a small bowl:
Sprinkle the mixture over the casserole and dot with:
Bake until the sauce is bubbling and the topping is golden brown, 25 to 35 minutes.