- 6 tablespoons unsalted butter
- 1 large onion or 2 leeks (white and light green part only), chopped
- 2 to 3 celery stalks, diced
- 3 garlic cloves, finely chopped
- 3 rosemary or thyme branches
- 2 bay leaves
- 3 ½ pounds mixed root vegetables (carrot, parsnip, celery root, turnip, rutabaga, sweet or regular potato), peeled and cut into 1-inch chunks
- 2 teaspoons fine sea salt, more as needed
- ½ teaspoon black pepper, more as needed
- Juice of 1/2 lemon, more for serving
- Extra-virgin olive oil
- Flaky sea salt
- Crushed Aleppo, Urfa or other chile flakes, optional
- Grated Parmesan or pecorino, optional
- Melt butter in a large, heavy-bottomed pot. Stir in onion and celery. Cook, stirring occasionally, until vegetables are tender, about 10 minutes. Stir in garlic, rosemary and bay leaves; cook 1 minute more. Add root vegetables, 8 cups water, salt and pepper. Bring to a boil; reduce heat to medium and simmer, covered, until vegetables are tender, 30 to 40 minutes.
- Remove and discard rosemary branches and bay leaves. Using an immersion blender, purée soup until smooth. (Alternatively, you can purée the soup in batches in a blender or food processor.) If the soup is too thick, add a little water. Season with lemon juice and more salt to taste.
- To serve, ladle soup into bowls and top with a drizzle of olive oil, a few drops of lemon juice, flaky salt and crushed chile or grated cheese, if desired.