Clean the clams thoroughly. Heat the oil in a pan large enough to take 3 times the amount of clams that you have. If you do not have a pan this large, do not worry; cook the clams in smaller batches, but start with all the stock, wine and vegetables. Add the vegetables to the oil and sweat until soft, then add the fish stock, white wine and parsley stalks and bring to the boil. When boiling, add the clams, cover and cook over a high heat until they open, stirring occasionally. This will only take 4 or 5 minutes. When cooked, tip the clams into a colander, and strain the stock through fine muslin. Allow the clams to drain until cold and then remove the meat from the shells.
Roll out the puff pastry on a floured surface to a thickness of about 5 mm/¼ inch. Using a
Cut the cucumber into fine strips about 4 cm X 3 mm/l½ X⅛ inch, using only the flesh and discarding the seeds in the middle. Pick the dill, reserve 6 nice sprigs as garnish, and roughly chop the rest.
Bring the stock to the boil, reduce by at least three-quarters, then add the cream and reduce until it thickens.