Rub butter into sifted flour and salt.

Add the sugar and currants.

Mix egg yolk and milk and then add to mixture and stir in well.

Roll out into a long, thin rectangle and place on a baking tray.

Beat egg white well and add icing sugar gradually. Spread thinly over the mixture that has been rolled out.

Score with a knife to create fingers.

Bake in a moderate oven for 20 minutes.