Put the egg yolks, sugar, and cornflour in a jug and mix them using a whisk until they make a single combination.
Then take your milk and your flavouring agent and warm them together on a pan. Don’t make them hot.
Take your warm flavoured milk and mix it with egg product in the first step, and put them back in the pan. Boil the mixture as you whisk all through the heating process.
After boiling, remove it on the heat source and continue with the whisking until you get a thick paste that sticks on the surface of your spoon. If it does not thicken, return it on heat and let it lose some of its water contents.
Notes
Depending on how you like it, you can serve it while hot or freeze it. A wrap will come in handy in case you want it cold to avoid forming a skin.