Place sifted matcha powder into a heat-safe jar or bowl.
Carefully add hot boiled water to the matcha.
Stir in sugar and milk powder and mix until everything is completely dissolved.
Heat whole milk and heavy cream in a small saucepan.
Bring to a simmer over medium heat and while whisking, gradually pour matcha mixture over a sieve into the saucepan. If there are any lumps remaining in the sieve, add some of the milk from the saucepan over top of the sieve and push through with the back of a spoon.
Whisk periodically until mixture has thickened and reduced by half, about 20 minutes over low-medium heat. It should be smooth and creamy.
A way to tell if it's ready is when you scrape the mixture in the pot with a spoon or whisk, there should be a line that is visible, meaning it has thickened enough. If you scrape the pot and can't see a line, continue whisking over heat.
Once it has thickened enough, remove from heat. Let cool.
Pour into a jar and refrigerate. The spread will be a little more thicker once it has cooled.
Best consumed in 1 week.