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 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 and the zest of your lemon. Pour in the boiling water or stock. Pop a lid on. Simmer 10 mins or till carrots are fully tender.
Blend till smooth, adding more water or stock, if needed. Add half of your chervil. Blend it through. Taste. Tweak seasoning as needed. Add a squeeze of lemon to add sharpness, if you like.
Divide between bowls. Garnish with the remaining chervil.