Warm a large pot over a medium heat. 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. Add to the pan. Drain your butter beans. Add them and the zest of your lemon. Crumble in your stock cube and 500ml boiling water. Cover and 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.