Crack the egg and separate the egg white from the egg yolk into two different bowls.
Add the sugar to the bowl with the egg yolk and whisk them together.
Put the milk into a pan and remove the vanilla seeds out of their pod. Add the vanilla and the pod into the milk.
Slowly bring the milk to a boil. The temperature of the milk should be 180 Fahrenheit but not higher then 185 Fahrenheit.
Just before the milk has reached 180 Fahrenheit, mix in the tapioca flour to the sugar mixture.
When the milk has reached 180 Fahrenheit, take the milk off of the heat. Slowly add the milk mixture to your egg-sugar mixture while whisking really well. Whisking is really important here!
When everything is whisked together, without any lumps, add the mixture back into the pan.
Let the custard simmer on low heat, for around 3-4 minutes, while constantly whisking.
After it has simmered for 3-4 minutes, remove the pot from the heat and remove the vanilla pod from the milk.
You can eat the custard warm, or if preferred, let it cool. It is important to stir during the cooling process, otherwise a film will form on top of the custard.