For the pastry, cream the butter and sugar together until light and aerated (best done with an electric mixer). Add the egg yolks one by one, and beat until well amalgamated. Add the sifted flour and salt and very gently knead into a dough without overworking. Shape into a slightly flattened ball, wrap in clingfilm and refrigerate for 1 hour.
Roll out the pastry on a lightly floured sur