Broccoli-Cheese Soup

2 cups water

1 small onion, chopped

3 stalks celery, chopped

2 chicken bouillon cubes

1 bunch fresh broccoli, chopped

1 stick butter or margarine

2 tablespoons flour

1 quart half and half

1 cup milk

5 American cheese slices

1/4 teaspoon salt

1/4 teaspoon pepper