Melt butter in dutch oven over medium heat.
Add onion and celery to butter and saute until onion is translucent.
Add garlic and continue to cook for an additional 2 minutes.
Add mushrooms and cook for an additional 10 minutes.
Add salt and pepper and stir.
Add 1 tbsp flour and stir cooking for 2 minutes.
Tie thyme together with cooking string.
Add broth, water, and thyme to pot and stir. Bring to a boil.
Cook for an additional 20 minutes.
Remove thyme bundle, any leaves that are still in pot are fine.
Using an immersion blender, puree soup.
Add cream and stir. Reduce heat and continue to cook for an additional 10 minutes stirring frequently.
