Sift the flour, baking powder and salt into a bowl, then add the butter and rub it in with your fingertips until the mixture resembles fine crumbs.
Stir in the sugar, and if you are making Sultana Scones, add them too. Add the milk and mix to give a soft dough; do not over-mix or the scones will be heavy. Cover the bowl with cling film and leave to rest for 30 minutes.
On a lightly floured work surface, roll out the dough to about 1.5cm thick. Cut out rounds with a 5.5cm cutter, re-rolling the trimmings where necessary. Place the scones on a baking sheet lined with baking parchment. Brush with the beaten egg and leave to rest for another 30 minutes.
Place in an oven heated to 180C/Gas Mark 4 and bake for 12-15 minutes, until well risen and golden brown. Transfer the scones to a wire rack to cool, and dust with icing sugar before serving.
