Preheat oven to 180C/160C fan-forced.
Melt the butter, golden syrup and sugar by stirring it all together in a small pan over low heat.
Pour the mixture into the bowl of a stand mixer and leave it to cool. (I usually put it in an ice-water bath for a while because I’m impatient.)
Once it’s cooled add the egg yolk and mix it through then add the rest of the dry ingredients and mix until the dough comes together.
Turn the dough out onto a piece of plastic wrap and shape it into a flat disc then pop it into the fridge for an hour to firm up.
Pre-heat the oven to 160C fan-forced and line two baking trays with baking paper.
Flour the bench and then, working with half the dough at a time, roll it out to 7-10mm thickness.
Trace around the template and cut out the dough then lay it out on the baking trays leaving a couple of centimetres between each one. Bake them for 7-10 minutes or until they start to firm. Leave them on the trays for a few minutes and then transfer them over to a wire rack to cool completely.
Meanwhile make the icing by beating the egg white until it starts to froth. Add the icing sugar and mix it in until smooth.
Divide it up into however many colours you want and tint them with colour.
Pipe an outline of colour around the edge of each biscuit and then pipe on a pattern. Leave it to set and then add the other colour. Use a bit of water if you need to thin out the icing.
Leave them until the icing sets then gobble them up with celebratory champagne when your horse comes in first.