In a small or medium pot, add milk. Turn the heat to low and warm up. Turn off before boiling.
In a bowl, add egg yolk and sugar. Mix well.
Add flour to the bowl by shifting. Mix everything.
Add the warm milk from the pot. Mix in the bowl and when the color is light yellow equally, put it back to the pot.
Turn the heat to low and stir contently.
It's getting thicker and heavier. When the mixture (custard) doesn't change the shape if dropping, it is time to turn off the heat.
After turning off, add vanilla bean powder. Mix thoroughly.
Move it to a container. Cool it down and after cooling down, put it to the fridge for 30 minutes.