Makes:4 to 6 servings
Healthy and extremely simple, this variation on the French classic soupe au pistou trades summer beans, squash, and tomatoes for winter cellar staples. Though parsnips, turnips, and celery root are often overlooked, their bright, clean taste and subtle sweetness are the perfect backdrop for the fresh, spicy watercress pistou.
3 medium turnips (about 1 pound), peeled and medium dice
2 medium parsnips (about 8 ounces), peeled and medium dice
2 bay leaves
1 medium celery root (about 12 ounces), peeled and medium dice
1 cup water
For the pistou:
4 ounces watercress, stems trimmed, washed, and dried
5 medium garlic cloves, coarsely chopped
1 tablespoon finely grated Parmesan cheese
1/4 cup olive oil
Freshly ground black pepper
For the soup:
Heat the oil in a medium saucepan over medium heat until shimmering. Add the onion, season with salt and pepper, and cook, stirring occasionally, until softened and just beginning to turn golden brown, about 5 minutes. Add the mustard, stir to coat the onion, and cook until fragrant, about 1 minute.
Add the remaining ingredients, season generously with salt and pepper, and stir to combine. Bring to a boil, then reduce the heat to medium low, cover, and simmer until the vegetables are tender, about 15 minutes.
For the pistou:
Meanwhile, combine the watercress, garlic, and Parmesan in a blender. Remove the small cap from the blender top, cover the hole with a kitchen towel, and turn the blender on. Remove the towel and add the oil in a slow, steady stream until evenly incorporated. Stop and scrape down the sides of the blender, then pulse until smooth. Taste and season with salt and pepper as needed.
Remove the soup from the heat and discard the bay leaves. Taste and season with additional salt and pepper as needed. Ladle the soup into serving bowls and top each bowl with a heaping teaspoon of the pistou.