1. Crush the plain cookies by hand or in a food processor, then tip into a mixing bowl.
2. Chop the nuts and sultanas by hand or place them both into the food processor together and pulse until chopped. (If you do the sultanas alone they will just fly around the sides of the bowl and not get near the blade).
3. Add sultanas, nuts, butter, cocoa, icing sugar, coconut, Rum to the mixing bowl, and mix well.
4. If the mixture is too wet, add a little more cookie crumbs (this can happen sometimes if the crumbs are processed too finely).
5. Roll into small balls, and roll these immediately into the extra coconut to coat.
6. The balls will be quite soft when made but will firm up once refrigerated for a little while.
7. Enjoy!