Preheat the oven to 200°C. Heat the olive oil in a large frying pan and flash fry the spinach in batches for 30 seconds. Transfer to a bowl. Cut the salmon into even sized pieces. Line the base of a 7 inch springform cake tin with some of the spinach. Arrange the salmon on top in an even layer and season the top well.
Pack more spinach on top and around the sides to enclose the salmon completely. Cut the pastry onto a 9 inch round and drape it on top of the spinach, tucking the sides in and around the sides of the cake tin. Brush all over with the beaten egg and prick the top a few times.
Bake for 20 minutes until the pastry is golden brown. Remove from the oven and leave to cool for 2 minutes before turning out and serving on a plate.