Heat the Milk: In a saucepan, heat the whole milk until steaming but not boiling. Turn off the heat.

Temper the Eggs: In a mixing bowl, aggressively whisk the egg yolks and sugar until pale and thick. Slowly drizzle a small splash of the hot milk into the egg mixture while whisking constantly to temper the yolks (preventing them from scrambling).

Cook the Custard: Pour the egg mixture back into the saucepan with the remaining milk. Cook over low heat, stirring constantly with a wooden spoon, until it thickens into a rich custard that coats the back of the spoon. Do not let it boil!

Add Matcha and Chill: In a small cup, whisk the matcha powder with 2 tbsp of warm water until it forms a smooth paste. Stir this paste thoroughly into the hot custard until uniformly green. Strain through a fine-mesh sieve. Let it cool completely.

Churn: Stir the cold heavy cream into the matcha custard. Chill the entire mixture in the refrigerator for at least 4 hours. Pour into an ice cream maker and churn according to the manufacturer directions until thick and frozen.