Heat oven to 180C/160C fan/gas 4.
Par-boil the potato slices for 2-3 mins.
Drain and set aside in a large bowl.
Gently fry the onion in the oil for
10 mins until lightly golden. Cool slightly,
then stir in the cream, crème fraîche,
herbs, zest and plenty of seasoning. Pour
over the potatoes and mix very gently.
Roll out one pack of pastry on a lightly
floured surface to a 35 x 35cm, then lay
on a large baking sheet. Pack ¼ of the
potato mixture down one side of the
pastry, leaving a 5cm border. Arrange
½ of the salmon on top to cover the
potato. Cover the salmon with ¼ of the
potato. Brush the pastry all the way
round with beaten egg and fold over the
pastry. Trim the edges and crimp with
your fingers, or seal with a fork. Make
decorative fish for the top, if you like.
Roll out the remaining pastry and
repeat the process, using up the rest of
the potato and salmon. Chill for 30 mins.
Brush the pastries all over with beaten
egg. Bake for 40 mins. Leave to rest for
10 mins if serving hot, or serve cold.