For the chocolate-orange cookies, mix flour, cornstarch and baking powder and sift into a bowl. Make a well in the center and mix in margarine, powdered sugar, egg, salt and lemon zest. Knead everything into a smooth dough.
Grate the chocolate and knead it in. Let the dough rest in the refrigerator for 1 hour.
Then roll out on a floured work surface and cut out stars. Bake on a greased baking sheet at 200° C for 10-20 minutes.
After baking, frost with an orange glaze.
Pour chocolate icing into a parchment bag, cut off tip and pipe rings onto chocolate orange cookies. Then use a wooden stick to pull through the icing to create a marble pattern.