Pike is a freshwater fish with a deep flavour that compliments the luxurious richness of crayfish here very well. It has many little bones, so be sure to remove them all before you start cooking.
For the sauce, place the crayfish heads and claws into a large saucepan and cover with cold water. Add the bay leaves and peppercorns. Bring to the boil and simmer for 20-30 minutes.
Add the raw tails to the pan and poach for two minutes then strain the liquid into a clean pan. Add the single cream, bring to the boil and reduce by one third. Remove the tails from the saucepan using a slotted spoon. Extract the flesh and set aside.
Stir in the mustard powder to the sauce and add the watercress. Return to the boil and simmer for two minutes. Place the sauce into food processor and blend until smooth. Pour the sauce into a clean pan and keep warm until needed.
For the pike, preheat the oven to 200C/400F/Gas 6.
Heat the oil in a frying pan over a medium to high heat. Add the pike fillets, skin-side down. Fry for three minutes, or until the skin is golden-brown.
Turn the fish over and cook for a further minute. Transfer the fish onto a baking tray and roast in oven for 6-8 minutes or until just cooked through.
For the sorrel, heat the butter in a large saucepan over a medium heat. When bubbling add the sorrel leaves and cook through for about two minutes, or until wilted.
To serve, place a small mound of wilted sorrel onto each plate. Top with a pike fillet, pour over the sauce and finish with three crayfish tails per person.
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