Rice, Mushroom & Sage Soup

I thought I had better squeeze in those last few winterish recipes before the hot weather sets in. It's been storming in Detroit the past week, so this soup was just perfect for a cozy meal. It is unique, creamy, hearty, and very satisfying. My friend, Melody, gave me this recipe and I really like it!
Note: I've only ever used the rubbed sage in it. I've done a generous tsp in the past, but I definitely don't think it's enough. I wrote 1 ½ tsp in the recipe, and next time I will experiment with 2 tsp.

Rice, Mushroom & Sage Soup
Submitted by Erin

1 small onion, finely chopped
3 large stalks celery, diced
25 large sage leaves finely chopped, or 1 ½ tsp rubbed sage
¼ c. flour
4 ¼ - 5 c. chicken stock (I use water with 4 bouillon cubes)
2/3 c. brown rice (raw)
8 oz. mushrooms, sliced
2 chicken breasts, cooked and shredded
¾ c. heavy cream
freshly grated parmesan cheese, to serve

Saute onion, celery and sage in a little butter over medium-low heat for 3-4 minutes, until the onion is somewhat softened. Stir in the flour and continue to cook for 2 minutes. Slowly add a quarter of the stock and stir well, scraping the bottom of the pan. Pour in the remaining stock (I would add 4 ¼ c, and more before serving if needed), stirring to combine completely, and bring just to a boil. Add rice, reduce heat and simmer gently, covered, for about 30 minutes, until the rice is just tender.
Meanwhile, saute the sliced mushrooms. Cook until they are golden brown, stirring occasionally at first, then more often after they start to color and create juice. Add the mushrooms to the soup, along with the shredded chicken. (I cook two frozen chicken breasts in the microwave at 50% power for about 25 minutes, then shred.) Stir in the cream. Continue simmering until heated through. Taste and adjust the seasoning, if necessary. Ladle into warm bowls and serve with parmesan cheese.