Melt the butter in a large saucepan over a medium-low heat. Add the leek and shallots, and cook,
stirring frequently, for 5 minutes, or until they start to soften. Add the cider and bring to the
Stir in the stock, potatoes and bay leaf with a large pinch of salt (unless the stock is salty)
and return to the boil. Reduce the heat, cover and cook gently for 10 minutes.
Put the flour in a small bowl and very slowly whisk in a few tablespoons of the milk to make a
thick paste. Stir in a little more milk to make a smooth liquid.
Adjust the heat so that the soup bubbles gently. Stir in the flour mixture and cook, stirring
frequently, for 5 minutes. Add the remaining milk and half the cream. Cook for a further 10
minutes, or until the potatoes are tender.
Finely chop the sorrel and combine with the remaining cream, Stir into the soup and add the
fish. Cook, stirring occasionally, for a further 3 minutes, or until the monk fish stiffens or the
cod just begins to flake. Taste the soup and adjust the seasoning, if necessary. Ladle into warmed
bowls and serve.