Process biscuit/cookies, either in a blender or put in a zip-lock bag and bash with a rolling pin. Finely chopped but doesn't have to be powder.
In a bowl, combine biscuits, coconut, milk and rum. Add cinnamon if using.
Shape the mixture into tablespoons of balls, place on baking paper and refrigerate until set.
If using pistachio, after shaping mixture into balls, roll balls in pistachio crumb, then refrigerate.