This light puree is more celery than potato. The potato thickens the soup, a simple potage that is brought to life by the tiny amount of walnut oil that’s drizzled onto each serving.
02Add the potatoes, garlic, and bouquet garni. Stir together and add the water or stock. Bring to a simmer, add salt to taste, cover and simmer 30 to 40 minutes, until the vegetables are very tender and the broth fragrant. Remove from the heat.
03Remove the bouquet garni from the soup. Using an immersion blender, puree the soup (or you can put it through the fine blade of a food mill or use a regular blender, working in batches and placing a kitchen towel over the top to avoid splashing). Then strain through a medium strainer (this step is important; otherwise the soup will be stringy), using a pestle or the bottom of a ladle to push the soup through. Make sure to scrape the outside of the strainer so that all of the puree goes back into the soup. Return to the pot, stir with a whisk to even out the texture, heat through and season well with salt and pepper.
04Ladle the soup into bowls and garnish each bowl with a few thin slices of celery and about 1/4 teaspoon walnut oil. Sprinkle with minced chives or chervil if you wish, and serve.