Method

Preheat the oven to 250°C.

Blanch the spinach leaves in boiling salted water for the briefest time, 5 – 10 seconds only. Drain and squeeze out the excess water.

Mix the herbs together. Put the sea salt into a food processor and crack it a little, then add the herbs and blitz until they are very finely chopped. If you have a Magimix put the flour, egg whites, salt and herb mixture into it and whiz to a green dough.

Otherwise, mix the flour and the salt and herb mixture well in a mixing bowl, then transfer to a clean work surface, pile up like a small mountain and make a well in the middle. Beat the egg white lightly in a bowl, then pour it into the well in the flour. Put in your hand and slowly and gently turn it, working in a little of the flour mix at a time, so that the egg white is absorbed gradually and forms a dough. Knead the dough for 3-4 minutes. If it feels too hard as you work it, wet your hands with a little water, which should help to loosen it. The dough needs to be firm and elastic enough to enclose the fish without breaking but not too loose, otherwise when it cooks it will release too much moisture, and the fish won’t cook properly. Wrap the dough in cling film and keep to one side.

Make the balsamic dressing: put the balsamic vinegar in a bowl, add the honey and sugar, and leave in a warm place, so that the honey and sugar can dissolve into the vinegar. Add the lemon juice, olive oil and cod sauce. Taste and, if you think it is too sharp, add a little more sugar to taste. Keep to one side.

Roll the dough out about 3mm thick. You need to cut this into 8 rough squares of dough – 4 to go beneath the fillets (make these about 2cm bigger all round than the fish) and another 4 to go over the top of each fillet to enclose them completely (these top squares will need to be about 3cm bigger all round than the fish). Each fillet will be slightly different, so use them as a guide when you are cutting out your dough.

Lay out the four squares of dough that will go underneath the fish and place a fillet on top of each, skin side facing upwards then brush the edges with egg wash and put the top square on top. Seal tightly and trim the edges neatly. Make sure there are no holes in the dough; if there are any, take a piece of the dough trimmings, wet it with water and use it to patch the hole. Brush with more egg yolk.

Line a flat ovenproof tray with baking paper, put the cod ‘parcels’ on it and place in the preheated oven for 7 – 12 minutes. Take one of the cod out and, with a sharp knife, cut around three sides, so you can lift up the crust like a lid, and check the fish inside. Press your finger against the fillet: if it is soft, then it is ready; if the flesh of the fish is resistant, then replace your ‘lid’ and put back in the oven until cooked. Remove the cod from the oven. Heat the spinach, stirring in the butter and olive oil. Season to taste.

To serve:

With a knife, cut the crusts and lift off the tops. Lift out the fish and put on top of the spinach. Finish with the balsamic dressing and serve.