Heat butter in a large pot over medium heat.
Add chopped sage and cook for 3-4 minutes. (This step can be skipped if not using sage).
Add diced yellow onion and minced garlic to the pot and cook until translucent, 2-3 minutes.
Add diced mushrooms, salt and pepper to the pot and cook until mushrooms are softened and have released their water. About 8-10 minutes.
While mushrooms are cooking, in a separate small saucepan, heat cream over medium heat.
Add bay leaves, nutmeg, half chopped onion, salt and pepper to the cream and gently simmer for 5 minutes (do not boil). Turn off heat once done simmering.
Once mushrooms are cooked (making sure the water from the mushrooms has reduced), add the chicken broth to the pot and simmer for 5 minutes. (If you are using other fresh herbs such as tyme, you can add them to the soup base now).
Once the mushrooms are done simmering. Remove the bay leaves, and chopped onion from the cream.
Slowly add the cream to the mushrooms and stir until combined.
Transfer the soup to a blender and blend until combined.
Serve warm and enjoy!
Note: Drizzle a bit of oil on top of the mushroom soup for additional flavor. Tarragon flavoured olive oil works nicely here.