Sift together the matcha and powdered sugar into a medium bowl, then set the mixture aside for a moment.

In a large mixing bowl, beat the softened unsalted butter on medium speed until it's creamy and smooth, which should take about 2-3 minutes.

Gradually add the sifted matcha sugar mixture to the butter, beating on low speed at first to incorporate the sugar, then increasing to medium to lightly whip the mixture. Continue mixing until the mixture is well combined and starts to look fluffy, with a bright green hue.

Pour in the vanilla extract and salt, and mix until they're fully incorporated into the frosting.

Add the milk or cream, one tablespoon at a time, beating well after each addition, only adding more liquid until you reach your desired consistency. The frosting should be creamy and spreadable, but still hold its shape.

Once everything is well combined, give the frosting a final whip on high speed for about 1 minute to add some extra fluffiness, then refrigerate or use it immediately.