Sauté the base
In a large pot over medium heat, melt butter or heat oil.
Add onion and cook 4–5 minutes until soft.
Add garlic and cook 30 seconds until fragrant.
Cook the mushrooms
Add mushrooms, thyme, salt, and pepper.
Cook 8–10 minutes, stirring occasionally, until mushrooms release their liquid and start to brown.
Thicken (optional)
Sprinkle flour over mushrooms and stir for 1 minute.
(This makes the soup extra creamy, but you can skip if you like thinner soup.)
Simmer
Pour in broth and bring to a gentle simmer.
Let cook 10 minutes to deepen the flavor.
Blend (optional but recommended)
Use an immersion blender to partially blend for a thick, cozy texture.
Or blend half the soup in a blender and return it to the pot.
Make it creamy
Stir in cream (or coconut milk).
Taste and adjust salt, pepper, and add a tiny splash of soy sauce or Worcestershire if you want extra depth.