1. Preheat the oven to 350 degrees F.
2. In a medium bowl, combine flour, baking soda, baking powder and salt, then set aside. In a separate bowl, whisk together milk and matcha until thoroughly mixed.
3. In the bowl of an electric mixer, cream together the sugar and butter, then add the eggs and vanilla extract. With the mixer on low, alternate by adding the flour mixture and matcha milk to the bowl and mix until smooth.
4. Line a cupcake or muffin pan with If You Care Large Baking Cups, then fill each baking cup three-quarters of the way and bake for 15-20 minutes. Remove from the oven and allow to cool.
5. While the cupcakes are cooling, you can start the matcha buttercream by combining the egg whites and sugar in the metal bowl of an electric mixer placed over a pot of boiling water to create a double boiler. Whisk over medium heat until the mixture reaches 160 degrees F on a thermometer.
6. Carefully remove the bowl and attach to the mixer, beating until the mixture appears light yellow. Once the mixture has cooled, slowly add the butter cubes, matcha powder and vanilla extract, making sure each addition is completely incorporated before adding more. Continue mixing until the icing becomes smooth and shiny, then spread the icing on the cupcakes or use a piping bag to create shape!