To make cookie dough, coarsely grate chocolate.
Beat butter or margarine, sugar, salt, egg and orange peel in a medium bowl.
Sift in flour and baking powder; add grated chocolate.
Knead ingredients quickly to a workable dough.
Press into a ball and wrap in foil or plastic wrap.
Refrigerate 30 minutes.
Preheat oven to 400 °F (205°F).
Grease baking sheets.
On a floured surface, roll out dough 1/4 inch (5 mm) thick.
Cut out 2-inch (5-cm) rounds.
Place on greased baking sheets leaving room for spreading during cooking.
Bake 10 to 15 minutes.
Remove from baking sheets with a spatula; cool on a rack.
To make frosting, put powdered sugar into a small bowl.
Beat in enough orange juice to give a coating consistency.
Spread frosting over cookies; let set.