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 ½ cup of mushrooms and finely chop (or blend with a little bit of liquid if preferred). Return to the soup with heavy cream.
Simmer 3 minutes more and serve.
