Place the onion, potato, oil, and butter in a medium sized pan and cook over a gentle heat until soft but cot colours about 5 minutes.
Add 500 ml boiling water and the chicken stock powder bring to the boil and then simmer for 10 minutes.
Place the haddock and egg white in a small food processor process until smooth, season with pepper and chill until required.
Add the spinach to the soup and cook for 1-2 minutes, then blend with a stick blender, or remove from the heat and puree the soup in a food processor or blender.
Return the soup to the heat, beat in the reserved egg yolk, and check the seasoning. Then use two small dessertspoons to create quenelles in round shaped dumplings.
Drop the quenelles into the soup and poach for 4-5 minutes.
Serve the soup one of two ways, for a dinner party:
Arrange 2-3 quenelles in a soup plate and pour in a little soup, garnish with the crème fraiche and a few rocket leaves. Serve the remaining soup in a serving jug and allow the guests to help themselves.
Alternatively serve in a large bowl or tureen with crusty bread for a family supper.
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