This is an easy, delicious soup from Anthony Bourdain’s Les Halles Cookbook. Recipe adapted from epicurious.com.
6 tablespoons butter (I use 3 tablespoons)
1 small onion, thinly sliced (I use 3/4 cup)
12 ounces/340 g button mushrooms, sliced (I use 16 ounces: 1 (8oz) package Cremini and 1 (8oz) package button
4 cups/900 ml light chicken (or vegetable) broth (I use 4 cups water with 4 tsp Better than Bouillon, Chicken)
1 sprig of flat parsley
Salt, to taste (at least 1/2 teaspoon Kosher salt)
Freshly ground black pepper
2 ounces/56 ml high-quality sherry (I skip this)
In a medium saucepan, melt 2 tablespoons of the butter (I use 1 tablespoon) over medium heat and add the onion. Cook until soft and translucent.
Add the mushrooms and the remaining butter (I use 2 more tablespoons). Let the mixture sweat for about 8 minutes, taking care that the onion doesn’t take on any brown color.
Stir in the chicken stock and the parsley and bring to a boil. Immediately reduce the heat and simmer for about an hour.
After an hour, remove the parsley and discard. Let the soup cool for a few minutes, then transfer to the blender and carefully blend at high speed until smooth. (Blending the soup really well at high speed is very important to ensure a creamy consistency, especially if cutting back on the butter. I tried using an immersion blender and it wasn’t able to blend enough to create the desired texture).
Return the soup to the pot, season with salt and pepper, and bring up to a simmer again. Add the sherry (if using), mix well, and serve immediately.