Place the butter, sugar, golden syrup, treacle, water and orange zest in a pan and heat gently while stirring until it is melted and smooth.
Remove the pan from the heat and beat in the spices and bicarbonate of soda, followed by the flour. Mix until it forms a smooth dough then cover the pan and place in the fridge for about an hour, until the dough is firm.
Preheat the oven to 180°C/350°F/gas mark 4 and line two baking trays with baking parchment. Bring the dough together into a ball and roll out on a lightly floured surface to about 3mm (⅛) inch thick.
Cut out shapes using cookie cutters and place them slightly spaced apart on the baking trays. Re-roll the scraps to cut out more shapes.
Place the trays in the freezer for 15 minutes until firm then bake for 10-15 minutes until the biscuits feel firm when lightly pressed and have begun to darken a little around the edges. The smaller ones will cook quicker than big ones so try to group similar sized ones together on the trays.
Leave to cool on the trays for 5 minutes then transfer onto a wire rack to cool completely.
Once the biscuits are cool, make the royal icing. Sift the powdered sugar into a bowl and add the lemon juice. Stir in the egg white a little at a time until the icing is smooth and thick but pipe-able; if you drizzle some back into the bowl the pattern should disappear after about 8 seconds. If it is too thick then add a little more egg white (or lemon juice if you've run out), and if it is too runny then add a little more sifted powdered sugar.
Spoon the icing into a piping bag fitted with a 1mm plain round nozzle. Pipe snowflake designs onto the biscuits (Pinterest is a great place to get inspiration for patterns!) and set them aside for half an hour to dry. Sprinkle with edible glitter if using.