Preheat the oven: Preheat the oven to 180°C (160°C fan)/350°F/gas mark 4.
Cream butter and sugar: Beat 75 g (3 oz) softened butter with 75 g (3 oz) golden caster sugar until light and fluffy, then beat in the egg yolk.
Add spices and fruit: Stir in ¼ teaspoon ground cinnamon, 50 g (2 oz) currants, and 15 g (½ oz) mixed peel. Mix to combine, then gradually add most of the 3 tablespoons of milk.
Make the dough: Mix in 175 g (6 oz) plain flour to form a stiff dough, adding the remaining milk if needed.
Roll and cut biscuits: Roll out the dough to 6 mm (¼ inch) thick and use a 7 cm (3 inch) round cookie cutter to cut out biscuits. Transfer them to a baking sheet, rerolling and cutting any trimmings.
Brush with egg white and sugar: Lightly beat the egg white and brush over the surface of the biscuits, then sprinkle with golden granulated sugar.
Bake: Bake for 15–18 minutes, or until the biscuits are pale golden. Allow to cool on a wire rack.