Cook onion & thyme in butter 3 minutes or until slightly soft. Add sliced mushrooms and cook until juices are released, about 5 minutes. Stir in garlic and cook 1 minute more.
Cook mushrooms 2 minutes while stirring. Add white wine and allow to cook down until almost evaporated (about 4-5 minutes).
Sprinkle flour over mushrooms and stir. Add chicken broth a little at a time until smooth. Add bay leaf and bring to a boil. Reduce heat and simmer 20 minutes uncovered.
Discard bay leaf. Remove about 1/2 cup of mushrooms and finely chop (or blend with a little bit of liquid if preferred). Return to the soup with heavy cream.
(Nutrition information provided is an estimate and will vary based on cooking methods and brands of ingredients used.)