In a stand mixer fitted with a paddle attachment, beat the butter and dark brown sugar until smooth and creamy. Scrape down the sides as needed.
Add in black treacle/molasses and vanilla, and crack in an egg as well. Beat the mixture together for 2 minutes until smooth.
In another bowl, whisk together plain flour, baking soda, ground cinnamon, ground ginger, all spice and ground cloves, along with a pinch of salt. Add this mixture to the wet ingredients and combine till a dough comes together. The dough will be a bit sticky, that's okay, just dust some flour in your hands and bring the dough together into a disk shape and wrap it in cling film and refrigerate for 1 hour.
Preheat the oven to 170 C. And line baking trays with parchment paper.
Dust the worktop with flour. Roll out the dough to about 1/4th of an inch and using a cookie cutter, cut out your desired shapes. Place the cut out shapes an inch apart from each other on the baking tray. Re-roll the scraps and repeat the process again to cut out the shapes.
Bake the biscuits for 10-11 minutes. Allow the biscuits to cool on the tray for 2 minutes before moving to a wire rack to cool completely.
For the royal icing
Whisk together icing sugar and egg whites. Add in water one tablespoon at a time till you get a smooth and flowy consistency to pipe. If you want to add food colouring, then divide the icing to different containers and add it at this stage.
Transfer the mixture into piping bags and snip off a tiny bit at the end. Decorate the gingerbread biscuits as desired.
These biscuits will stay fresh in an air tight container for up to a week.