Clean, wash and chop the leek and celery. Peel and finely dice onions and garlic. Peel, wash and roughly dice the potatoes. Fry everything except 1⁄3 garlic in 3 tablespoons of oil. Add 1 1⁄2 l water, broth and bay leaf, bring to the boil and simmer for about 5 minutes. Add frozen spinach, bring to the boil and simmer for about 15 minutes.
Wash the parsley and pluck the leaves. With the rest of the garlic, lemon juice and 2 tablespoons of oil, puree finely. Season gremolata and soup with salt and pepper. Serve with toasted bread.