These chocolate biscuits are lightly flavoured with coffee and gorgeously iced with South American colours and patterns.
Make the biscuits. Beat together the butter and sugar in a stand mixer fitted with the beater attachment on medium speed, for about 2 minutes, until pale and light.
Add the egg, coffee and golden syrup and mix again until smooth and thoroughly combined.
Sift the flour and cocoa powder into the bowl and mix again to combine. Using your hands, shape the mixture into a smooth ball, flatten into a disc, cover, and chill for about 1 hour, until firm.
Lightly dust the work surface with flour and roll out the biscuit dough to about 3mm thick. Using the cutter, stamp out as many shapes as possible (re-roll the trimmings as necessary), arranging them on the lined baking sheets as you go. Chill the biscuits for 20 minutes and heat the oven to 180°C/160°C fan/Gas 4.
Bake the biscuits for about 12 minutes, until firm, then remove from the oven and leave to cool completely on the baking sheets.
Reduce the oven temperature to 120°C/100°C fan/Gas ¼.
Make the icing. Tip the egg yolks into separate bowls and add 1 teaspoon of milk to each bowl. Add a drop of red food-colouring paste to one bowl and of blue paste to the other. Mix each well to thoroughly combine.
Paint half the biscuits with red glaze and the other half with blue and bake in the oven for 2 minutes, until the glaze is dry. Repeat this glazing twice more, then remove the biscuits from the oven and leave to cool completely.
Tip the egg whites and icing sugar into a stand mixer fitted with the whisk. Whisk on medium speed, until the mixture is thick, glossy and holds soft peaks. Add the glucose and lemon juice and whisk again to combine.
Divide the icing between four bowls: tint one yellow, one red and one green and leave the fourth bowl white. Spoon the icing into the piping bags fitted with the fine writing nozzles and pipe geometric patterns over the biscuits. Leave to set firm for at least 1 hour before serving.