For the biscuits: Place the flour, bicarb, ginger, cinnamon and unsalted butter into the bowl of a food processor. Blend until the mixture looks like breadcrumbs, then pulse in the sugar until combined. Or if you don't have a food processor, rub the butter into the dry ingredients using your hands until it resembles breadcrumbs. Then whisk in the sugar until combined.
In a separate bowl, lightly beat the egg and golden syrup together and then pour into the food processor. Pulse until the mixture clumps together. Or, using a wooden spoon mix the wet ingredients in with the breadcrumb mixture until it clumps together.
Tip out the dough onto a lightly floured surface, and knead until combined and smooth. Wrap the dough in clingfilm and pop it in the fridge for 15 minutes to firm up.
Preheat the oven to 180C/160C Fan/Gas Mark 4 and line two baking trays with baking paper. Roll the dough out to 0.5cm thickness on a lightly floured surface. Cut out circles and stars (or any other festive shape you like) and place on the baking trays leaving a little gap between them.
Bake for 12-15 minutes or until golden-brown. Leave them on the baking tray for 10 minutes and then place them on cooling racks to cool completely.
For the icing: Mix the icing sugar with two/three tablespoons of water until you have a thick icing. You want it to be thick enough so that it doesn't run off the biscuits when you decorate. Pour the icing into a piping bag, and snip off the end so you are left with a small hole to pipe from.
Decorate your biscuits as you wish, and leave to set at room temperature.
Notes
The biscuits can be kept stored in a sealed container for at least a week.