Make the salsa ahead of time and keep it cold. 15 minutes before serving, remove the dish from the fridge. Set aside.
In a large pan or wok, combine the spinach, butter, and nutmeg, along with seasonings. Place over a low-medium heat and cover with a lid. Allow the spinach to wilt slightly, then mix thoroughly and cook, stirring occasionally, until the spinach has entirely wilted (about 5 minutes). To remove the liquid, sieve it. Allow it cool slightly before squeezing any extra liquid from the spinach between sheets of kitchen paper.
Cooked spinach should be roughly chopped. Combine the crème fraîche and lemon juice in a mixing bowl. Add seasoning to taste and set aside.
Using a medium burner, heat a frying pan. Lightly toast the almonds for 3-5 minutes, tossing frequently, until golden. Roughly cut the ingredients.
Using flour, lightly dust a surface. Roll out the puff pastry to a size of 30cm x 50cm (12in x 20in). For the ornamentation, cut a 5cm (2in) strip off the short end, then cut the huge rectangle in half across the length. One half should be large enough to cover the salmon fillet, so gently roll it out (this will be your top piece).
On a nonstick baking sheet, place the smaller piece of pastry. Place one half of the fish on top of the other. Place a layer of spinach on top, followed by the chopped almonds. Place the second half of the salmon on top of the first, with the thicker end over the thinner end.
Brush beaten egg around the edges of the pastry around the salmon. Place the second piece of puff pastry on top and seal the edges. Neaten the edges by cutting a long, sharp knife through the pastry's very edge, then crimping with two fingers. Using a beaten egg, brush the surface.
The remaining strip of puff pastry should be rolled out. To decorate the top of the pastry, cut out holly leaves or stars. Using a beaten egg, brush these as well. Before baking, chill the dough for 20 minutes.
Place the tray in the preheated oven's center and bake for 30-35 minutes, or until golden. Slice along the width to