Measure and put flour, salt, soda, and baking powder in sifter. Cream margarine / butter & adding sugar gradually. Then eggs one at a time. Add vanilla & peppermint. Mix cocoa in boiling water and leave to cool. On low speed add the flour mixture until all mixed in well, along with the cocoa liquid. Pour ¼ of mixture into prepared tin, add some coins then more mixture, etc. Bake at 160ºC (325ºF) for about 30-45 minutes or until cooked. Remove from oven, invert & leave to cool before removing from tin. Slice into 3 layers and spread with peppermint frosting between layers and on top & sides.