Cut each muffin into 4 pieces and line a 1.2L (2 pt) serving bowl. Place muffins in the bowl.
Mix custard, cocoa and sugar in a medium saucepan with a little of the milk. When combined add rest of the milk and mix well. Carefully bring mixture to the boil, stirring all the time, and simmer for 1 minute.
Pour mixture slowly over the muffins. Be careful, if using a glass dish. Lay cling film on chocolate custard or sprinkle a very light dusting of caster sugar on top, to prevent skin forming, while cooling. Cool for approximately 1 hour, then chill in fridge until completely cold.
Whip the double cream until stiff and use to decorate the trifle. Sprinkle with crumbled chocolate flakes and serve.
* Trifle can be made the night before.
* For Adults try: Spoon a little espresso or coffee liqueur over each muffin before pouring on custard and decorate with chocolate coated coffee beans.