01 -
Cook spaghetti according to package directions. Drain and set aside.
02 -
In a Dutch oven, melt butter over medium heat. Stir in flour, salt, and white pepper until smooth. Gradually add chicken broth, half-and-half, and heavy whipping cream. Bring to a boil; cook and stir until thickened, about 2 minutes.
03 -
Remove the cream sauce from heat. Stir in cooked chicken, drained mushrooms, and drained pimientos. Add cooked spaghetti to the mixture and toss to coat evenly.
04 -
Divide the mixture evenly into two greased 11x7-inch baking dishes. Sprinkle each casserole with grated Parmesan cheese.
05 -
For immediate serving, bake one casserole uncovered at 350°F for 20-25 minutes, or until heated through. To freeze the second casserole, cover and store in the freezer for up to 2 months.
06 -
To reheat a frozen casserole, thaw it in the refrigerator overnight. Cover and bake at 350°F for 30 minutes. Uncover and bake for an additional 15-20 minutes, or until heated through. Stir before serving.