Preheat oven to 180°C bake (160°C fan-forced). Line two baking trays with baking paper.
Place the flour, baking soda, ginger and sugar in a bowl or food processor. Add butter and rub in with fingertips or pulse in food processor until it resembles fine breadcrumbs. Add egg and golden syrup and stir or pulse to mix. If the dough is sticky, add a little more flour until it forms a workable dough. Wrap in plastic wrap and refrigerate for 30 minutes.
Roll out on a lightly floured surface or between two sheets of baking paper until 5mm thick. Cut out shapes using biscuit cutters and place on trays. Form leftover dough into a ball and re-roll and repeat cutting out until dough is used up.
Bake for 8-10 minutes until golden brown. Cool on a wire rack.
Make icing by beating egg white with a fork until frothy. Fold in the other ingredients and place icing in a resealable bag. Snip off the corner and pipe decorations onto each biscuit. Use icing to attach lollies or currants.