Meanwhile, in 4-quart Dutch oven, melt butter over medium heat. Cook shallots, celery, salt and pepper in butter 6 to 8 minutes, stirring occasionally, until tender. Increase heat to medium-high; add mushrooms, and cook 6 to 8 minutes longer or until mushrooms release juices and begin to brown. Stir in chestnuts and stock; heat to simmering. Cook 2 to 3 minutes, stirring frequently, using spoon to release browned bits from bottom. Remove from heat; cool 5 minutes.