Preheat the oven to 200C (180C fan) and line two large baking sheets with parchment paper.

In a large bowl, cream together the butter and 75g of caster sugar until the mixture is light and fluffy.

Beat in the egg yolk until fully incorporated.

Sift the flour, cinnamon, and mixed spice into the bowl and mix until a crumbly dough begins to form.

Stir in the currants and add enough milk to bind the mixture into a soft dough.

On a lightly floured surface, roll out the dough to a thickness of approximately 5mm.

Use a 7cm fluted round cutter to stamp out biscuits and place them onto the prepared baking sheets.

Bake in the preheated oven for 8 minutes.

Remove from the oven, brush the tops of the biscuits with the lightly beaten egg white, and sprinkle with additional caster sugar.

Return the biscuits to the oven for a further 5 to 7 minutes until they are golden brown.

Transfer the biscuits to a wire rack to cool completely.