Method
In a large pot, melt butter and cook mushrooms with a pinch of salt for 15 minutes on medium-high heat. Stirring often.
Add onion and cook for 4 minutes or until soft and translucent. Add garlic and stir for 1 minute. Stirring often.
Tie thyme sprigs and parsley into a small bundle with kitchen twine then add into the pot.
Add broth and bring to a boil then lower the heat. Simmer the soup, uncovered, for an hour, stir occasionally.
Remove the parsley and thyme bundle from the soup.
Let the soup cool for a few minutes then carefully blend the soup in a blender or using an immersion blender.
Return soup to pot and stir in dry sherry. Simmer for 3-5 minutes on medium-low heat. Add salt/pepper if necessary.
Turn off the heat. Serve and enjoy with pan-fried mushrooms and/or toasted French baquette.
Notes
If you want to avoid alcohol, skip the dry sherry. This soup will taste delicious with or without the dry sherry.