Preheat the oven to 180C/350F/Gas mark 4
Cream together the icing sugar and margarine until light. Work in the flours and knead thoroughly. Form the mixture into a roll. Then roll into the demerara sugar until well coated. Refrigerate for at least an hour. Cut into ¼ inch slices and place the Cookies on an ungreased baking tray. Bake them for at least 10 minutes. Watch very carefully that the edges dont burn. Cool on a wire rack.