CELERIAC, POTATO, LEEK AND APPLE SOUP

Steps:

• Heat the olive oil in a large, heavy soup pot over medium heat and add the onion, leeks and a pinch of salt. Cook, stirring, until tender, about 5 minutes. Add the celeriac and a generous pinch of salt, cover partially and cook for another 5 minutes, stirring often, until the celeriac has begun to soften. Add the potatoes, apples, water or stock, salt to taste, and the bouquet garni. Bring to a boil, reduce the heat, cover and simmer 1 hour, or until the vegetables are very tender and the soup is fragrant. Remove and discard the bouquet garni.
• Blend the soup in batches in a blender (cover the top with a towel and hold it down to avoid hot splashes), or through a food mill fitted with the fine blade. The soup should be very smooth. Strain if desired. Return to the pot. Stir and taste. Adjust salt, add freshly ground pepper, and heat through. Serve in small bowls or espresso cups, garnished with thin slivers of celery leaves.