You will need a large frying pan and a baking sheet with a liner or lightly greased
Place the frying pan on a high heat then add the butter followed by the green salad leaves and wilt it for about 1 minute, stirring it around until it has collapsed then tip it into a sieve over a bowl and leave it to cool.
Then use the back of a wooden spoon to press the wilted greens against the sieve and extract any juices.
Now place it on a chopping board and press with several sheets of kitchen paper to extract any wetness that remains. Spoon it into a small bowl then stir in the crème fraîche, lemon juice, some freshly grated nutmeg and some seasoning.
Divide the rested pastry into 4 even pieces then roll the first piece very thinly into a oblong the same shape as the salmon fillet, roughly 21cm by 15cm (you will need to adjust the size of the pastry to according to the shape of the salmon fillet).
Then spread a quarter of the wilted greens mixture about the same size as the fillet, in the centre of the pastry then place a salmon fillet on top.
Using a pastry brush dampen the corners of the pastry with cold water the fold the pastry in over one of the shortest edges of the salmon first and then do the same with the opposite side.
Now dampen the pastry along the edges that still need to be folded in, then fold them in over the salmon, overlapping and enclosing the salmon like a parcel. Carefully turn the parcel over and put it onto a parchment lined tray.
Do the same with the remaining salmon fillets then pop them in the fridge until you need them.
If you are preparing them in advance cover them with a piece of cling film.
When you are ready to bake them, pre-heat the oven to 220°C, Gas Mark 7.
Place the parcels on the baking sheet, with a liner, then make 3 diagonal slashes in each one and brush each one with beaten egg. Bake for 20 minutes on a high shelf until crisp and golden.