First make the royal icing: In a stand mixer, or with an electric whisk, whisk together all the ingredients until a smooth thick paste is formed.
Using a closed star nozzle pipe individual trees onto lined baking sheets, top each with a star decoation and scatter with a few sprinkles for the baubles. Leave in a cool dry place to dry and harden, which will take up to 24 hours
Once the icing trees have set, make the shortbread tree trunks: Preheat the oven to 170 degrees centigrade. Line a baking sheet with parchment
Sift the flour into a bowl and stir in the sugar and vanilla. Add the dairy-free margarine and rub in with fingers. Once it starts to combine, press together to form a soft dough.
Sandwich the dough between two sheets of baking paper, roll out the dough to 1cm thickness. Place in the fridge to rest and chill for at least half an hour.
Using a small circular cookie cutter, stamp out circles and transfer to the lined baking sheet. You should make about 80 ’tree trunks'
Bake for 10 minutes until the biscuits are starting to turn golden. Remove from the oven and then cool on a wire rack.
Once totally cool, mix together 5ml (1 tsp) water with 40g icing sugar to make a thick water icing, and use this to attach the tree tops to each mini shortbread tree trunk. Leave to set.
These keep beautifully for at least 1 week.