Roll pastry 1/2 in thick and cut into fingers 4 in by 1 in Spread top thinly with royal icing.
Bake in a hot oven (425°-450° F., Gas 7-8) until pastry is well risen and icing lightly browned.
Allow to cool.
Slit carefully through the centre, spread bottom half with jam.
Pipe or spread whipped cream over the jam and sandwich the two halves together again.