Beat the butter and dark brown sugar in a bowl until creamy, about 3 minutes. Stir in the molasses, egg, and orange zest and continue to beat for 1 minute.
Combine the flour, cocoa powder, bicarbonate of soda, spices, and a pinch of salt in a separate bowl. Add to the butter and egg mixture and continue stirring to make a smooth dough. Leave to rest in the refrigerator for about 1 hour.
Preheat the oven to 180˚C (350˚F). Butter a mini muffin tray and dust with flour. Shape the dough into 36 walnut-sized balls. Press the balls flat between your palms and use them to line the muffin holes. Bake the cookie cups for 10 minutes, being careful not to brown them. Remove from the oven and, if necessary, press the hot cookie cups further into the moulds to make a larger hollow in the middle.
Place 1 teaspoon grated chocolate into each hollow and allow to melt. Use a pastry brush to spread the melted chocolate over the insides of the cookie cups. Leave them to cool.