1 tablespoon unsalted butter
1 cup finely chopped onion
2/3 cup finely chopped celery
3/4 teaspoon freshly ground black pepper
1/4 teaspoon salt
3 (8-ounce) packages presliced mushrooms
1/2 cup + all-purpose flour (about 2/3 cup)
3 (14.5-ounce) cans fat-free, less-sodium chicken broth
3+ cups grated fresh Parmesan cheese, divided
1/2 cup (4 ounces) 1/3-less-fat cream cheese
7 cups hot cooked vermicelli (about 1 pound uncooked pasta)
4 cups chopped cooked chicken breast (about 1 1/2 pounds)
1 (1-ounce) slice bread
1. Preheat oven to 350°.
2. Melt butter in a large stockpot over medium-high heat. Add onion, celery, black pepper, salt, and mushrooms; sauté 4 minutes or until mushrooms are tender. Add sherry; cook 1 minute.
3. Weigh or lightly spoon flour into dry measuring cups; level with a knife. Gradually add flour to pan; cook 3 minutes, stirring constantly (mixture will be thick) with a whisk. Gradually add broth, stirring constantly. Bring to a boil. Reduce heat; simmer 5 minutes, stirring frequently. Remove from heat.
4. Add 2 1/2 cups Parmesan cheese (or more if needed) and cream cheese, stirring with a whisk until cream cheese melts. Add pasta and chicken; stir until blended. Divide pasta mixture between 2 (8-inch-square) glass or ceramic baking dishes coated with cooking spray.
5. Grate or food process bread into crumbs. Combine breadcrumbs and ˝ cup Parmesan cheese; sprinkle evenly over pasta.
6. Bake at 350° for 30 minutes or until lightly browned and bubbly. Remove casserole from oven; let stand 15 minutes.
To freeze unbaked casserole: Prepare through Step 5. Cool completely in refrigerator. Cover with plastic wrap, pressing to remove as much air as possible. Wrap with heavy-duty foil. Store in freezer for up to 2 months.
To prepare frozen unbaked casserole: Thaw casserole completely in refrigerator (about 24 hours). Preheat oven to 350°. Remove foil; reserve foil. Remove plastic wrap; discard wrap. Cover casserole with reserved foil; bake at 350° for 30 minutes. Uncover and bake an additional 1 hour or until golden and bubbly. Let stand 15 minutes.