Put olive oil in a heavy-bottomed pot or Dutch oven over medium-high heat. Add leeks and parsnips, and stir to coat. Add the 2 teaspoons salt and pepper to taste.

Let vegetables sizzle and cook, stirring frequently until nearly caramelized, but without browning, until softened, 10 to 15 minutes.

Add bay leaf, turmeric and garlic, and stir to coat. Increase heat to high, add water or broth, and bring to a boil. Reduce heat to a simmer and cook for 10 minutes more. Taste broth and adjust seasoning.

With a blender, purée soup to a creamy consistency. (Small batches work best.) Thin with water or broth, if necessary — it should be like a thin milkshake, not thick and porridge-like.

Reheat the soup before serving. Serve plain, or give each bowl a drizzle of extra-virgin olive oil or a dolop of crème fraîche or yogurt, if desired.