Soften butter and beat with sugar. Continuing to beat, add the egg and milk. Separately sift flour and cocoa powder, mix with egg mixture. Knead soft dough.
On a lightly floured board, roll out the dough to a 5mm thickness.
Preheat oven to 180°C. Using cookie cutters, cut out circles from the dough. Grease two baking sheets with oil, line with parchment and lay out the cookies. Bake 10-12 minutes. Leave for 15 min. on a baking sheet, then transfer to a wire rack and let cool completely.
Mix powdered sugar with orange juice. You should get a thick mixture.
Break the chocolate into small pieces with your hands and, stirring, melt in a water bath.
Spoon the orange icing over the cooled cookies and let set. Garnish with thinly sliced orange slices. Then shade with melted chocolate in thin strips.