Posh fish pie

1. Heat the butter in a pan and sweat the shallots and fennel until soft. Add the wine and vermouth and reduce by half. Add the stock and bubble away again until reduced by half.
2. Pour in the cream and boil until reduced to a sauce like consistency. Strain through a sieve, discarding the shallot and fennel. Stir in the mustard, check for seasoning then leave to cool.
3. Meanwhile heat the oven to 180°C/gas 4. Check the fish for any small bones, removing any with tweezers, then cut into 3cm chunks. Poach the fish in enough water to cover, with a squeeze of lemon juice and the thyme, until slightly undercooked. Remove the fish from the poaching liquid with a slotted spoon. Gently fold the prawns and fish into the sauce with a little extra lemon juice and chopped herbs. Transfer to an ovenproof baking dish.

For the topping

1. Cook the potatoes in boiling salted water until tender, and mash with a little milk and butter until smooth. Beat in the egg yolks, then either pipe the mash over the filling or spoon it over for a more rustic finish.
2. Bake the pie for about 20 minutes until bubbling and golden brown on top. Serve with buttered petit pois or spinach.