Peel and take out the seeds of the custard apples.
Peel and chop the dragon fruit.
Put the fruit into a blender with enough milk to make up to approximately 1.20 - 1.50 litres in your blender and blend until smooth.
Keep your milkshake in the fridge. We prefer to put ours in the freezer for half an hour before we drink it as the kids prefer the slightly thicker consistency.