Luxury Fish Pie with Rosti Caper Topping

First of all, 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.

Meanwhile, heat the wine and fish stock in a medium saucepan, add the bay leaf and some seasoning, then cut the halibut in half if it's a large piece, add it to the saucepan and poach the fish gently for 5 minutes. It should be slightly undercooked. Then remove the fish to a plate, using a draining spoon, and strain the liquid through a sieve into a bowl.

Now 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 you have a smooth sauce, 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 it from the heat.

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. Now remove the skin from the white fish and divide it into chunks, quite large if possible, and combine the fish with the sauce.

Next, if you're going to cook the fish pie more or less immediately, all you do is add the raw scallops and prawns to the fish mixture then spoon it into a well-buttered baking dish. 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 on a high shelf of the oven for 35-40 minutes.

If you want to make the fish pie in advance, this is possible as long as you remember to let the sauce get completely cold 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're ready to cook it.

Then give it an extra 5-10 minutes' cooking time.