To make the custard, I followed the instructions on the back of the box itself and found it worked quite well with a few tweaks to the steps. First, dissolve the custard powder in 1/2 cup milk in a small bowl and set aside. Then in a saucepan, stir the sugar into the remaining 1 cup milk and bring to a simmer on low heat.
Into this, pour in the custard powder+milk mixture slowly and whisk constantly (a balloon whisk is great here). In a few seconds the mixture will begin to thicken. Cook for about 2 minutes till it coats the back of a spoon and when you run your finger through it, there should be a trail left on the spoon.
Turn off the heat and let the custard cool for about 30 minutes, before transferring to the fridge for 1 hour or till completely chilled. A skin will inevitably form on top so you can skim off the top just before serving or stir it in like I do. (You can also press clingfilm directly to the surface to prevent the skin from performing but I prefer to avoid plastic in contact with hot food.)
Before assembly, add the chopped fruit to the custard and stir it all together.
Now break up the biscuits into half (or smaller pieces depending on the dish you're using) and place two to three pieces in the base of small glasses or jars. Top with a little custard, then repeat until all the biscuits pieces and custard are used up. Place in the fridge for 30 minutes to let the biscuits soften a bit, then dig in!
The trifle pudding is best eaten immediately after chilling, but it will keep in the fridge for 2 to 3 days, though the biscuits will soften more with time. Happy trifling!