Shells with Mushroom Cream and Cheese - serves 6

1 pound medium or small shells, uncooked
1 tbsp cornstarch
1 1/2 cups milk, divided
1/2 cup chicken broth, homemade or canned
Salt and ground pepper to taste
1 cup frozen peas, defrosted
1 4 ounce can sliced mushrooms, drained
1/4 cup sliced pimentos
2 cups diced cooked chicken, optional
3/4 cup grated Parmesan cheese, plus more for passing
1/4 cup unseasoned bread crumbs

Prepare pasta according to package directions; drain. Rinse the pasta under cold running water until cool and drain thoroughly. Preheat oven to 350F.
In small bowl, stir together the cornstarch and 2 tbsp of the milk until the cornstarch is dissolved. Heat the remaining milk and the chicken broth in a small saucepan over medium heat. Stir in the cornstarch mixture and heat, stirring, until the sauce is simmering and thickened.
Add the salt and pepper and simmer 3 minutes. Pour the sauce into a bowl, add the peas, mushrooms, pimentos, chicken if using, 1/2 cup of the Parmesan cheese and the cooked pasta. Stir the sauce in until it and the vegetables are evenly distributed. Transfer to a baking dish. Stir 1/4 cup of the Parmesan cheese and the bread crumbs together in a small bowl and sprinkle the mixture over the pasta. Bake until the sauce is bubbling and the topping is golden brown, about 15 minutes. Serve hot, passing additional grated Parmesan cheese if desired.