Provided by: Chef Thomas Keller
Cut the bottom half of the stem off each cèpe and cut the base into a 1/4-inch dice. Slice the remaining cèpe into sixths from top to bottom and reserve.
Heat 2 tablespoons oil in a medium saucepan. Add the diced mushroom stems, garlic, and onions, and sweat until the onions are translucent. Add the thyme, stock, and cream, and bring to a boil. Mix 1/4 cup of flour with the butter in a small bowl to form a paste. Remove the saucepan from the heat and slowly whisk in the butter-and-flour mixture until incorporated. Return the sauce to a simmer and cook gently for 15 minutes, whisking constantly to prevent the bottom from burning. Season with salt, pepper, and lemon juice.
Bring 7 quarts of water to a boil, add kosher salt, and return to a fast boil. Add haricots verts and blanch until tender, 2 to 3 minutes. Drain the beans and chill in ice water. Drain again, and dry the beans on paper towels.
Add 1 quart oil to a large saucepan and heat to 325 degrees. Holding the shallots at the root end, slice very thinly on a mandoline. Place the shallots in a mixing bowl, add the flour, and toss together until the shallots have separated into rings. Add all the shallots to the saucepan at once and fry, stirring constantly, until they are lightly browned. Drain, place on paper towels, and season with salt.
To finish, preheat the oven to 350 degrees. Sauté the reserved cèpes in 2 tablespoons oil until golden brown. In a large bowl, combine the cèpes, cream of cèpe, and haricots verts. Check the seasoning and adjust accordingly. Transfer to an ovenproof casserole dish and bake uncovered for 15 minutes. Sprinkle parsley and the crispy shallots on top.(Published 2005)