In a large bowl, add the flour, sugar and mixed spice. Stir to combine.
Add the butter and rub into the dry ingredients with your fingers until the mixture resembles fine breadcrumbs. Add the currants and mix.
Add the [beaten] egg and the milk, and mix to form a fairly stiff dough - you may need to use your hands to do this. If your dough feels too dry, add a little extra milk.
Tip the dough onto a floured surface and gently knead for a moment to bring together.
Heat a frying pan or flat griddle pan over a low-medium heat. Leave to come to temperature whilst you prepare your Welsh Cakes.
Using a rolling pin, roll the dough to about 5mm thick and cut into circles with a round 7cm cookie cutter. Set each circle to one side once cut and continue to re-roll the dough until you have around 12-15 round cakes.
Lightly grease your frying/griddle pan before placing your cakes on, keeping a bit of space between them (be careful not to overcrowd your pan - you will need to do this in batches). Cook the cakes for 3-5 minutes on each side, or until golden brown in colour.
Place the cooked Welsh cakes onto a wire rack to cool and dust with a little caster sugar to finish.
Welsh Cakes will keep for about 1 week, stored in an airtight container.