Get a large pot hot. Scrub or peel your carrots. Finely dice the carrots and celery. Finely chop the onion.
Gloss your heated pot with 1tbsp oil. Add the diced veg. Season well. Sizzle over medium-low heat till just tender.
Finely chop your garlic. Cook a mo. Drain your butter beans. Add them, the zest of your lemon and the boiling water or stock. Cover. Simmer for 10 mins or till the carrots are fully tender.
Blend till smooth. Add more water or stock, if needed. Add half your chervil. Blend it through. Taste. Tweak seasoning as needed. Add a squeeze of lemon, if you like.
Divide between bowls. Garnish with the remaining chervil.