Half a liter of butter
1 minced little onion

oil from olives, 1/4 cup
1 pound of sliced mushrooms (any kind, including portobello, cremini, button, etc.)

Two garlic cloves, mincedSeason to taste with salt and pepper.
Boil 3 cups of chicken or vegetable stock.
A 1.5-quart measuring cup of heavy cream; 1 tablespoon of all-purpose flour may be added for thickening purposes.
For decoration, you may add chopped fresh parsley.
Steps to take:
In a large saucepan, melt the olive oil and butter over medium heat. Brown the mushrooms. Simmer, stirring often, for 8 to 10 more minutes or until the sliced mushrooms begin to brown and release their juices.
Aromatherapy for Flavor: To soften, sauté the chopped onion for about 5 minutes. After a minute or two, stir in the minced garlic and thyme, and keep cooking until they release their aroma. Season to taste with salt and pepper.
On the other hand, a Roux is an option: Simmer, whisking constantly, for a another minute or two as the mushrooms cook. This will cause the soup to thicken.
Slowly add the broth and mix well, stirring regularly. To let the flavors to blend, simmer for 10–15 minutes after the ingredients reach a boil.
You may use an immersion blender or carefully pour some of the soup into a blender to smooth it up if you like.
While stirring, slowly heat the heavy cream or half-and-half, being cautious not to boil. To taste, adjust the salt and pepper seasoning.
Spoon the soup into each dish before serving, and if desired, garnish with chopped fresh parsley.
Enjoy a bowl of this velvety mushroom soup on chilly evenings.