Heat the oven to 200*C. (180*C in a fan oven), 400*F, gas 6.
Heat the honey with the sugar and butter, stirring continuously until the sugar has dissolved. Remove from the heat and pour into a mixing bowl. and allow to cool.
When cooled add the almonds, flour, cocoa, lemon zest, cinnamon, gingerbread spice and the egg. Kneed well using and electric whisk with dough hooks.
Dissolve the potash in the rum and stir into the dough until it shines and is no longer sticky. If it is too soft add some more almonds. The dough should be firm and malleable. Cover and allow to rest overnight in the fridge.
The next day roll out the dough on a floured surface approx. 1 cm thick and cut out heart shapes. Place the hearts on a baking tray lined with grease-proof paper and bake for 15-25 minutes (depending on their size).
Remove carefully from the baking try as they will still be very soft. Place them on a wire rack to cool. Once they are completely cooled decorate them with writing sugar and allow to dry.