Chicken-Macaroni Casserole

3 cups cooked elbow macaroni
2 cups grated American cheddar cheese
1 1/2 cups cooked chicken, cubed
1 cup sliced canned mushrooms
1/4 cup diced pimiento
2 Tbsp. butter
2 Tbsp. flour
1/2 tsp. pepper
2 cups milk

Arrange macaroni and cheese in alternate layers in buttered 2 quart casserole. Combine chicken, mushrooms and pimiento. Make a well in center of macaroni and fill with chicken mixture. Melt butter, blend in flour, salt and pepper, gradually add milk. Cook, stirring constantly, until thickened. Pour over mixture in casserole. Bake at 350 degrees for 1 hour.