In a saucepan, heat up milk and heavy cream until a slight boil and turn off heat
In a separate bowl, combine egg yolks, sugar, vanilla extract and whisk until creamy and fluffy
Add in cornstarch and matcha and whisk until combined. Make sure there aren't any clumps.
In small increments, add in 1/4 at a time of the hot milk mixture in the egg mixture and whisk. You want to slowly add in as you whisk so you don't cook the egg yolk mixture all at once because that can lead to clumping
Once the egg and milk mixture is combined, pour mixture into the saucepan and turn on the stove to low heat. Continue to mix thoroughly to prevent uneven cooking.
Slowly, the mixture should start to thicken up. This will take a few minutes. You should get a thick custard mixture.
Remove from heat, place in a bowl, and into the fridge to cool.