During his years captaining El Bulli, Ferran Adrià was the master of the head fake—a dish that signals one thing only to move in a different direction. I love the sense of surprise and delight when your brain tells you one thing but your mouth tells you another. It’s just an instant, but in that single bite you experience a whole range of human emotion. (Sorry if I sound a little worked up, but a good dish will do that to me.) Serve this mushroom cappuccino in nice coffee cups on saucers and watch people work through the delicious surprise.
SERVES 4 TO 6
4 tablespoons unsalted butter
1 medium onion, finely chopped
2 garlic cloves, finely chopped
1½ pounds button mushrooms, trimmed and roughly chopped
Kosher salt
5 cups water
1½ cups heavy cream
2 sprigs thyme
Finely ground coffee
Melt the butter in a large saucepan, over medium heat. Add the onion and garlic and cook until softened and golden, about 10 minutes. Add the mushrooms, turn the heat to high, and season with salt. Cook, stirring, until mushrooms are lightly browned, about 15 minutes. (They will release a lot of liquid at first, but it will boil off.)
Add the water, cream, and thyme sprigs to the mushrooms. Bring to a boil, then reduce the heat and simmer until the liquid reduces by half, about 40 minutes.
Discard the thyme sprigs. Working in batches if necessary, transfer the soup to a blender and carefully pulse about ten times to break the mushrooms down and release their juices. Strain the soup through a fine strainer into a clean saucepan, pressing on the solids to extract as much liquid as possible. Reserve the solids for garnish; rinse out the blender.
Bring the soup to a boil. Pour the soup back into the blender and blend it well—the goal is to introduce as much air as possible, as if you were aerating milk for a cappuccino. (You can also use an immersion blender for this, holding it near the surface of the soup to aerate it as much as possible.)
Pour the soup into coffee cups and garnish each one with a pinch of ground coffee.