2) Place a piece of cod on a roasting tray on a piece of greaseproof paper. Push the crab topping firmly over the cod and place the roasting tray in the oven until lightly browned, 10 to 15 mins.
3) Blanch the potatoes in boiling water. Gently soften the leeks and spring onion in the remaining butter. Add the potatoes and vegetable stock and bring to the boil. Reduce by half, add the cream, a good pinch of salt and pepper and a pinch of chopped parsley.
4) Spoon the potatoes and leeks onto a plate and top with the cod.