2 medium leeks
1 tablespoon oil
2 cloves garlic, finely chopped
4¼ cups vegetable stock
1 teaspoon sea salt
1 head romaine (or other) lettuce
¼ cup fresh tarragon
black pepper, freshly ground
lemon juice to taste
lemon zest to taste
plain yogurt, to garnish, optional
1. Thoroughly wash the leeks and slice them into half circles, discarding the root end.
2. Heat in a large saucepan over medium heat and add the oil. Add the leeks and garlic and cook, stirring often, until softened and just beginning to turn golden, about 10 minutes.
3. Add the stock and salt and bring to a simmer. Turn heat to low, cover, and simmer for 15 minutes to soften leeks further.
4. While the soup base is simmering, slice the whole head of lettuce crosswise into 1-inch thick stripes and discard the base. Wash the lettuce and drain it in a colander or salad spinner.
5. Stir the lettuce into the soup, increase heat to medium, and cook, uncovered until the lettuce is wilted and softened, about 45 minutes.
6. Stir in the tarragon leaves (you may want to use less if you want a lighter tasting soup). Puree the soup in batches in a blender or use an immersion blender) until very smooth. When the soup is blended, return to the pan and gently reheat. Taste and season with salt, pepper, lemon zest, and lemon juice.
7. Optional garnish – Vigorously stir yogurt, adding tiny amounts water until it falls off the spoon in a thick stream. Hold a spoonful about 6 inches above the bowl and let it fall in a circular or zigzag pattern on the soup.