Make the puff pastry and chill it 30 minutes. Put the cream and lemon zest in a small saucepan. Scald, remove from the heat and leave to infuse, 10-15 minutes. Trim roots and wash the samphire. Blanch it in boiling salted water 2 minutes and drain.
Cook the onion in the butter until soft but not brown. Add the flour and cook 2-3 minutes. Strain in the cream, of