Preheat oven 400 degrees. grease two large cookie sheets. set aside. Put the butter and all but a tablespoon of the sugar into a large bowl and cream until pale and fluffy. Beat in the egg yolk, then add the flour and mix well. Stir in enough milk to form a smooth dough.
Roll out the dough on a lightly floured work surface. Cut out rounds using a 3 inch cookie cutter. Arrange the circles on the cookie sheets, leaving enough space between then to allow them to spread during cooking. Sprinkle over the remaining sugar and bake for 15 minutes or until golden. Remove the cookies from the oven, transfer to wire racks and let cool completely.
To make the frosting, put the confectioners sugar and cocoa powder into a bowl. Stir in the orange juice gradually until enough has been added to make a thin frosting. Drizzle over cookies using a spoon dipped in the icing.