1. Make chocolate brownies according to box mix instructions. Allow to cool and then cut into small squares. Cut some very small squares for decoration on top of the triffle.
2. Pour custard into a saucepan with the dark chocolate and gently heat. Stir until all the chocolate has melted and is mixed into the custard. Allow to cool.
3. Pour the double cream into a bowl and add the icing sugar then whip the cream with an electric whisk until it forms soft peaks.
4. Take your trifle bowl and add a layer of brownies. In the gaps add some of the Malteasers and chocolate stars. Pour half the chocolate custard onto the brownies then add another layer of brownies, malteasers and stars and pour on the remaining chocolate custard.
5. Pour on the cream, you can keep some back to pipe around the edge. Decorate with brownies, malteasers and chocolate stars.
6. Refrigerate. Enjoy!