Old-school French chefs are serious about sweating vegetables for soups. Farm-fresh vegetables at their peak, slowly sweated in the right fat, can become a glorious soup, with nothing but water to adjust viscosity. We take sweating a touch further here, rounding out the almost citrusy aroma of celery root with chicken broth and fresh thyme. (This makes a heck of a vegetable puree if you use 2 cups of broth. Think of it as an alternative to mashed potatoes.) Serve with slightly charred rustic--preferably multi-grain--bread rubbed with garlic and spritzed with olive oil.