Preheat the oven to 180°C and line a tray with baking paper.
Cream the butter and treacle sugar until fluffy and combined. Mix in the egg.
Sift in the flour, cinnamon, cloves, ginger, salt and baking powder. Mix until the ingredients come together and form a dough. Wrap the dough in plastic wrap and refrigerate for at least 30 minutes.
Lightly dust your work surface and rolling pin with flour. Roll the dough out to a thickness of 3mm. Cut out your shapes and arrange them on the baking tray. Use a skewer to make a hole at the top of each biscuit.
Pop the tray in the oven and bake the biscuits for 10-12 minutes, or until the edges start to turn golden. Transfer to a cooling rack and leave to cool completely.
To make the icing: whisk the egg white for a few seconds until foamy. Sift in 1 cup of icing sugar and beat in. Sift in the remaining icing sugar. Add the water and mix well. If the icing is too thick add more water a few drops at a time. The icing should have a soft, piping consistency but not be too runny.
Pipe or drizzle the icing over the biscuits. Decorate and leave to dry. Once the icing has set tie the thread through the holes and hang the biscuits on the tree.