1.Place biscuits in a food processor and pulse until fine crumbs form. Transfer to a large bowl. Add coconut and drinking chocolate. Stir in butter, then condensed milk.
2.Mix well. Stir in rum. Chill for at least 30 mins, or up to 24 hours.
3.Roll teaspoons of mixture into small balls. Roll balls in cocoa to coat. Store in an airtight container in the fridge until ready to serve.