Place an oven rack in the middle position. Preheat oven to 350 degree F. Line a 12-cup muffin pan with cupcake liners.

In a large bowl, stir the butter, sugar, matcha and salt until combined. Whisk in the egg whites, one at a time, until each is incorporated. Whisk in the milk and vanilla.

Add the flour and baking powder to the bowl, then whisk until just combined.

Spoon the batter into the cupcake cups and bake until just firm, about 17 minutes.

Let the cupcakes cool in the pan for 5 minutes, then transfer to a wire rack to cool completely before frosting.

In a large bowl, heat the chocolate with the cream, whisking gently, until the chocolate is melted and the mixture is smooth.

Whisk in matcha, then chill the ganache until it’s spreadable, about two hours, stirring occasionally.

Spoon a rounded tablespoon of ganache onto each cupcake.