Chop the chocolate. Knead quickly with the remaining ingredients to form a smooth dough. Wrap in foil and chill for about 30 minutes. Preheat the oven to 180 degrees (convection 160 degrees, gas level 2). Roll out the dough between two layers of parchment paper and cut out hearts. Spread on a baking sheet lined with baking paper. Bake for about 10 minutes until light brown.