Chicken and Rice Casserole

This is a really good casserole made with ingredients you probably already have at home. I used chicken breasts instead of a whole chicken. It doesn't take that long to make either, which is great for weeknights. Makes 8 servings.

1 (4 pound) whole chicken
1 onion, quartered
2 stalks celery
2 bay leaves
1/3 cup butter
8 tablespoons all-purpose flour
2 cups milk
1 cup chicken stock
2 cups shredded Cheddar cheese
1 (4.5 ounce) can sliced mushrooms
1 cup cooked white rice
salt and pepper to taste

In a large pot boil the chicken with the onion, celery and bay leaves until done. Let chicken cool until you can handle it. Remove chicken meat from the bones and cut into small pieces.
Preheat oven to 375 degrees F (190 degrees C).
In a saucepan over medium heat melt the butter. Stir in the flour and cook for about 1 minute. Slowly stir in the cold milk and chicken stock and cook mixture until thick. Stir in the cheese.
In a large bowl combine the chicken, rice and mushrooms together. Stir in the cheese sauce and season with salt and pepper. Place mixture in a 1 1/2 quart casserole dish.
Bake at 375 degrees F (190 degrees C) for about 30 minutes or until bubbly.