This recipe is from Food Network.
½ sticks (1/4 cup or 4 tablespoons) of butter
1 onion, peeled and chopped
2 celery root, peeled and chopped into small pieces
1 ½ L chicken or vegetable broth
1 tsp dried thyme or fresh thyme
Salt and pepper to taste
In a 4-quart saucepan, sauté the onion in the butter until it just begins to caramelize. Add the celery root, chicken broth, thyme, salt and pepper and bring to a simmer. Cook until the celery root is tender, about twenty minutes. Smoothly puree the soup with an immersion blender, a counter-top blender or a food processor.