Mix the flour, cocoa and a pinch of salt in a bowl. Beat the butter with the sugars in another bowl for about 3 mins until pale and creamy. Stir in the egg and vanilla. Gradually mix the dry ingredients into the wet, and bring together with your hands. Wrap the dough and leave to chill in the fridge for 1 hr.
Heat the oven to 170C/150C fan/ gas 3. Roll out the dough on a lightly floured work surface to a thickness of about 4mm, and press out circles in three sizes. Place them, sorted by size, on baking sheets lined with baking parchment. Bake the smallest cookies for 6-8 mins and the remainder for about 10-12 mins. Remove from the oven and transfer to a wire rack to cool completely.
Tip the icing sugar into a small bowl and gradually add the milk, stirring until smooth and thick. Coat the tops of the biscuits with it using a small knife, then stack three of each biscuit, starting with the largest. Cut the cranberries into small pieces and stick to the snowmen as eyes, mouths and buttons. Cut the strips of mango into the shape of mini carrots, and place them on the faces as noses. Leave to dry. Will keep in an airtight container for up to three days.Recipe adapted from Let it Snow by Agnes Prus (£7.99, Hardie Grant). Photographs © Frauke Antholz.