Rub the butter into the flour until the mixture looks like breadcrumbs, then stir in the sugar, currants and mixed spice.
Add the beaten egg and enough of the milk to bring it together into a soft dough that is firm enough to roll. Handle it lightly, like a scone mix.
Roll out on a floured surface to about 1 cm thick and cut into rounds with a 6 to 7 cm cutter. Re-roll the trimmings until you have about 12 cakes.
Heat a flat griddle or heavy frying pan over a low to medium heat and wipe with a little butter. Cook the cakes for about 4 minutes per side until golden with a mottled brown speckle, adjusting the heat so they cook through without burning.
Cool slightly on a wire rack and dust generously with caster sugar while still warm. Best eaten the same day, split and buttered.