Peel and finely chop the onion. Trim and finely chop the celery. Trim, peel and finely chop the carrot. Warm 2 tsp oil in a pan over a low heat. Add the chopped veg. Season with salt and pepper.
Cover and cook the veg for 8-10 mins till soft but not coloured. Stir now and then. If the veg start to catch, turn the heat down or add a splash of water.
While the veg cook, peel and dice the potatoes. Add them to the pan. Crumble in the stock cube. Pour in 800 ml boiling water. Cover and turn the heat up to bring it to the boil.
When the chowder is boiling, turn the heat down to medium. Simmer for 15 mins till the potatoes are tender.
While the chowder simmers, remove the leaves and silks from the sweetcorn cob. Lay the cob down on a chopping board. Carefully cut down the sides, rotating as you go, to slice off the kernels. Add them to the pan. Simmer for 2-3 mins to just cook them.
Ladle half the chowder into a blender. Add in half the crab meat and 2 tbsp of the crème fraîche. Blend till smooth. No blender? Ladle half the chowder into a bowl and blitz with a hand-held blender, or mash with a potato masher.
Pour the blitzed soup back into the pan. Add in the rest of the crab. Gently heat for 1-2 mins to just warm through. Taste and adjust the seasoning. Ladle into warm bowls. Serve topped with an extra ½ tbsp crème fraîche each and some chopped chives.