Clean mushrooms with a damp cloth and slice, discarding tough stems.
Heat butter in pot over medium heat. Add onions and cook until translucent (5-7 minutes).
Add garlic and mushrooms. Cook until mushrooms release moisture and begin to brown (8-10 minutes).
Pour in stock, bring to boil, then reduce to simmer for 15 minutes.
Add half-and-half, thyme, salt, pepper, and nutmeg. Simmer 5 more minutes.
Optional: Blend half the soup for a creamier texture.
