Pour 3 Tablespoons olive oil into a 12-inch sauté pan and heat
it over medium-low heat. Add the shallot and sauté until softened
but not browned, 2 to 3 minutes. Add the mushrooms and lemon juice and
sauté until the mushrooms release their juices, 10 to 12 minutes.
Season with salt and pepper to taste and set aside.
Put the celery, thyme, chicken stock, chestnuts, and 1 cup water in a
heavy-bottomed, 2-quart saucepan and bring to a boil over medium heat.
Lower the heat and simmer for 12 minutes. Remove the chestnuts from the
pot with a slotted spoon and set aside, covered to keep warm. Reserve
Put the pancetta in the same 12-inch pan and heat
it over medium-high heat until it gives off enough fat to coat the bottom
of the pan. Add the Brussels sprout slices and cook until lightly browned,
approximately 1 1/2 minutes. Add the mushrooms and chestnuts and toss
to warm through. Season with salt and pepper to taste. Transfer to a bowl