1. Using only the white and light green part, cut the leeks in half. Place under running water to rinse off any grit/dirt. Then, chop into medium dices. Set aside.
2. Peel and cut the celery root into medium dices. Set aside.
3. Cut the fennel bulb in half. Remove the core and cut into medium dices. Discard or reserve the fronds for another use.
4. In a large soup pot over medium heat, add the olive oil. When hot, add the leeks and sauté until slightly soft, about 4 minutes. Add the garlic and cook another 2 minutes.
5. Add the chopped celery root and fennel.
6. Add 6 cups of the stock and all the milk. Cook until vegetables are soft and tender, about 25-30 minutes. Remove from heat. Let cool slightly.
7. In a food processor or blender, and working in batches, puree the vegetables and liquid until a very smooth consistency.
8. Return the soup to the pot. If soup is too thick, add the remaining cup of stock. Season with salt & pepper.
9. Reheat the soup before serving.
10. Ladle into soup bowls, drizzles a little olive or pistachio oil on top of soup. Sprinkle a little chopped pistachios on top and serve immediately.
TIPS & TRICKS
• While they are from the same plant family, apium graveolens, celery root or celeriac is not interchangeable with celery stalks. Celery root has a strong celery flavor with hints of parsley and a nutty twist. Their appearance is kinda ugly, all gnarled and brown. But the inside has the texture of a potato. They are a great addition to soups and stews.
• Purchase celery roots that are a little on the heavy side. If available, the size of a grapefruit, or 3 smaller ones.
• Soup can be made 2 days ahead.