2 tablespoons margarine
1 tablespoon olive oil
2 large leeks (white and pale green
parts only), thinly sliced (about 2 cups)
1 large onion, chopped
2 medium-size Yukon Gold potatoes
(about 12 ounces), peeled, cut into
1-inch cubes
2 medium celery roots (celeriac; about
1 1/2 pounds total), peeled, cut into
1/2-inch cubes
2 large fresh thyme sprigs
1 bay leaf
8 cups low-salt chicken broth
5 celery stalks with leaves, stalks
thinly sliced, leaves reserved
1/3 cup whipping cream
Melt butter with oil in heavy large pot over medium heat. Add leeks and onion and sauté until almost tender, about 10 minutes. Stir in potatoes, celery roots, thyme, and bay leaf. Add broth and bring to boil. Reduce heat, cover, and simmer until vegetables are tender, about 40 minutes. Add celery stalks and simmer until all vegetables are very tender, about 12 minutes longer. Cool slightly. Using handheld blender, puree soup in pot. Stir cream into soup. Season to taste with salt and pepper. (Can be prepared 1 day ahead. Cover and chill celery leaves. Cool soup slightly. Chill uncovered until cold, then cover and keep chilled. Rewarm soup over medium heat before serving.) Ladle soup into bowls. Garnish with reserved celery leaves and serve.
