1 Sieve the flour onto the work surface. Make a well in the centre and add the butter, sugar, egg and a pinch of lemon zest. Quickly knead into a smooth dough that comes away from the hands easily. Wrap in cling film and chill for approx. 30 minutes.
2 Heat the oven to 200°C (180°C in a fan oven), 400°F, gas 6 and line a baking tray with grease-proof paper.
3 Roll the dough out onto a floured surface to a thickness of approx. 3 mm and cut out shapes, e. g. stars or boots. Place on the baking tray and bake in the oven for 10-12 minutes until golden. Remove from the tray and leave to cool.
4 To decorate, whisk the egg white with 1 tsp lemon juice until stiff. Trickle in the icing sugar and beat to form a firm, shiny icing. Spread the icing over the cooled biscuits, then spoon the remaining icing into a piping bag. Allow the iced biscuits to dry slightly, then decorate with spots using the remaining icing. Leave to dry completely.