In a large pot, melt the butter, when hot, add the onion, celery, carrots, and mushrooms. Stir oftern and cook until the onion softens. (I used Shiitake mushrooms - stems removed, and did not have celery on hand so just skipped that.)
Stir in the garlic, salt, parsley, thyme, sage, and pepper. Cook for just a minute or two until the garlic is fragrant.
Add the chicken breasts, rice, and broth. Stir together and heat to a boil. Reduce heat, and simmer 15 minutes, stirring occasionally.
Then remove the chicken to a cutting board and chop, and set aside. Let to soup continue to simmer.
When the rice is tender, about 10-15 minutes after you took the chicken out, return the chicken to the chicken to the pot and simmer for another 5-10 minutes to heat the chicken through. Taste and add salt as desired.
Ladle into bowls, serve, and enjoy.