Make the custard by warming the milk on medium heat. Add the sugar and custard powder to a small bowl with a bit of water and make a paste. Take a bit of the milk and add it to the mixture. Add this to the milk when the milk almost reaches boiling point and stir all the time. Let it thicken while stirring continuously. Set aside to cool down completely. A good store-bought custard can work as well, but it must be a good type made with full cream milk.