Preheat large heavy bottom pot or Dutch oven on medium heat, add butter and wait until it has melted. Add onion and garlic; saute for 3-4 minutes.
Add carrots, celery, fresh mushrooms (if using), thyme, garlic powder, salt and pepper; saute for 5 minutes.
Add chicken, potatoes, dried mushrooms (if not using fresh), wild rice, water/broth.
Cover, bring to a boil, then reduce heat to low and cook for about 55 minutes.
Remove chicken onto plate and shred with 2 forks.
To the pot, add milk and mustard. Using an immersion blender give a few pulses until soup is desired thickness (don’t forget to stir and feel free to adjust thickness with extra water and spices).
Add shredded chicken and parsley, stir well.
Serve hot with crusty bread for dipping.
