Rub the butter into the flour to make breadcrumbs. Add the sugar and sultanas, then stir in the egg. Mix, then form a ball of dough, using a splash of milk if needed.
Roll out the dough on a lightly floured surface until it is 5mm/¼in thick. Cut it into rounds using a 7.5cm/3in fluted cutter.
You now need a bakestone or a heavy iron griddle. Rub it with butter and wipe the excess away. Put it on a direct heat and wait until it heats up. Place the Welsh cakes on the griddle and cook for 2–3 minutes on each side, or until caramel brown.
Remove from the pan and dust with caster sugar while still warm. Some people leave out the sultanas, split them when cool and sandwich them together with jam.