Heat a large dutch oven or heavy bottomed pot over MED heat. Add olive oil and butter. Add mushrooms, garlic, onion, carrots and celery, and cook, stirring occasionally, about 5 minutes, until soft.
Stir in salt, pepper, and thyme. Add flour and stir to coat, cooking 1 minute. Stir in chicken stock, scraping bottom of the pan to loosen the browned bits.
Add potatoes and bay leaf, and bring to a low boil. Boil for 12-15 minutes, until thickened and potatoes are fork tender. If chowder is getting too thick, add additional chicken stock or water as needed.
Stir in cream and shredded chicken and cook 2 minutes, or until heated through. Taste and adjust seasonings as necessary, then serve.
