Fish pie jackets

Method

1. Heat the oven to 200°C/180°C fan/gas 6. Prick the potatoes all over with a fork, then rub with oil and salt. Bake on a baking tray for 1 hour or until cooked through. When cool enough to handle, cut roughly 2cm off the top of each potato (reserve to serve as skins). Scoop out the potato flesh into a bowl, leaving a 1cm potato shell. Mash the flesh with 50g butter and season. Set aside.
2. Warm the milk in a medium pan with the bay and peppercorns, then add the fish and prawns and poach for 3 minutes or until just cooked. Transfer the fish and prawns to a plate using a slotted spoon and keep warm. Discard the bay/peppercorns and reserve the poaching milk.
3. Melt the remaining butter in a separate medium pan and whisk in the flour. Cook for 3-4 minutes, then slowly whisk in the wine and reserved poaching milk. Simmer, stirring, for 10 minutes until thickened. Add the lemon zest and juice (to taste), herbs and mustard, then stir in the fish and prawns.
4. Spoon the fish and sauce into the potato shells and top with the mash and cheese. Put on a baking tray with the crispy potato skins on the side and bake for 20 minutes until piping hot and the cheese is golden.