Preheat oven to 180°C (350°F).

Line baking sheets with parchment paper.

In a large bowl, cream together softened butter and caster sugar until light and fluffy.

Gradually beat in the beaten egg.

In a separate bowl, sift together flour and mixed spice.

Stir in lemon zest and currants or sultanas.

Gradually add the dry ingredients to the butter mixture, mixing until a dough forms.

Knead the dough lightly on a floured surface until smooth.

Roll out the dough to about 1cm thickness.

Cut out shapes using cookie cutters.

Place biscuits on the prepared baking sheets.

Brush the tops of the biscuits with milk or beaten egg.

Sprinkle with caster sugar.

Bake for 15-20 minutes, or until golden brown.

Let cool on the baking sheets for a few minutes before transferring to a wire rack to cool completely.