Add butter, honey, sugar, molasses, gingerbread spice, cocoa powder, and salt to a pot over medium heat and stir to combine. Keep stirring until the sugar is dissolved, then remove from heat and let cool down.
Sift flour and baking powder into a large mixing bowl. Add egg and butter-honey mixture and knead until a smooth dough forms. Cover with a kitchen towel and let rest for at least 7 hrs.
Preheat oven to 200°C/390°F. Roll out dough on a silicone baking mat or in between two sheets of plastic wrap. It should be 1-cm/0.4-in thick. Cut out ten heart-shaped forms and transfer them onto two parchment-lined baking sheets. Bake in the oven for approx. 12 – 15 min. Remove from oven and transfer onto a neutral underground when still warm. Let cool down completely.
For the icing, add egg whites to a large mixing bowl. Sieve confectioner’s sugar into the bowl, then beat until fluffy and stiff. Divide into three parts and add red and green food coloring to one part each. The third part stays white.
Transfer all three icings into separate piping bags with tips. Decorate gingerbread hearts as desired and enjoy for yourself or as a gift!