1 Prepare the potatoes by scrubbing them, but leaving the skins on. As they all have to cook at the same time, if there are any larger ones cut them in half. Then place them in a saucepan with enough boiling, salted water to barely cover them and cook them for 12 minutes after they have come back to the boil, covered with the lid. Strain off the water and cover them with a clean tea-cloth to absorb the steam.
2 Meanwhile, heat the wine and stock in a medium saucepan, add the bay leaf and some seasoning, then cut the fish into large pieces, add them (not the prawns and scallops) to the saucepan and poach gently for 5 mins. The fish should be slightly undercooked.
3 Remove the fish to a plate, using a draining spoon, and strain the liquid through a sieve into a bowl.
4 Rinse the pan you cooked the fish in, melt the butter in it, whisk in the flour and gently cook for 2 minutes. Then gradually add the strained fish stock little by little, whisking all the time. When the sauce is smooth, turn the heat to its lowest setting and let the sauce gently cook for 5 minutes. Then whisk in the crème fraîche, followed by the cornichons, parsley and dill. Give it all a good seasoning and remove from the heat.
5 To make the rösti, peel the potatoes and, using the coarse side of a grater, grate them into long shreds into a bowl. Then add the capers and the melted butter and, using two forks, lightly toss everything together so that the potatoes get a good coating of butter.
6 Now remove any skin from the white fish and divide it into large chunks and combine the fish with the sauce. Next, if you are going to cook the pie more or less immediately, add the raw scallops and prawns to the fish mixture then spoon it into the well-buttered baking dish.
NB If you want to make sure everyone gets their fair share you can add the sauce to the dish before adding the fish, which can be inserted in the sauce, positioned appropriate to the planned servings.
7 Sprinkle the rösti on top, spreading it out as evenly as possible and not pressing it down too firmly. Then finally scatter the cheese over the surface and bake at 220°C on a high shelf for 35-40 minutes.
Cook now, eat later:
TO PREPARE AND COOK AHEAD
Prepare as above, but allow the sauce to cool completely before adding the cooled white fish and raw scallops and prawns. When the topping is on, cover the dish loosely with clingfilm and refrigerate it until you are ready to cook it. Then give it an extra 5-10 minutes' cooking time.
Recipe based on 'Seafood in Winter'
in Delia Smith's 'Winter Collection'