In a small-sized saucepan, boil the milk and Thai tea leaves. Turn off the heat and let it infuse for 30 minutes. Strain the mixture with a fine sieve into a bowl.
In a medium-sized saucepan, measure 156g of the infused Thai tea milk and boil it with half of the sugar.
In a medium-sized bowl, whisk the egg yolks and the remaining sugar. Temper the egg