Grease a 6 inch round cake pan or 6 inch springform pan with butter. Cut a 6 inch circle of parchment paper and 2 strips of parchment that will cover the sides of the pan. Grease one side of each strip with butter to ensure that the cake will NOT stick. Place the parchment round in the bottom of the cake pan and stick the non-greased side of the strips to the side of the pan. Cover the outside of the pan with foil then place this contraption inside a larger (8-9 inch) cake pan. Preheat the oven to 390 degrees F (about 200 degrees C).
In a small bowl, mix 50 grams (¼ cup) of sugar and the matcha powder together until there are no matcha lumps.
In a separate large glass bowl, heat the cream cheese and butter in the microwave (30 seconds at a time) until the butter is melted and the cream cheese is soft. Whisk together until smooth. Add the GF flour and cornstarch and whisk until there are no lumps. Add the matcha sugar and whisk until smooth. Pour in the milk and mix until a nice batter forms. Over a medium-sized metal bowl (or bowl of a stand mixer), separate the egg whites from the yolks and place the all three yolks into the matcha batter. Whisk the yolks into the matcha batter until smooth.
Using a hand mixer, beat the egg whites until frothy. While the mixer is running, slowly sprinkle in the remaining 50 grams (¼ cup) of sugar. Keep beating on high until medium stiff peaks form.
Add half of the meringue to the matcha batter and fold (using a whisk) it into the batter, being careful not to deflate all the air in the meringue. Add the rest of the meringue and carefully fold in, switching to a spatula halfway through, until everything is combined and still fluffy.
Pour the batter into the prepared cake pan and gently tap a couple times on the counter to release large air bubbles. Pour the boiling water into the larger pan (about ¾ full) and carefully place the cake pan contraption into the oven. Bake for 20 minutes, then (without opening the oven door) lower the heat to 360 degrees (182 degrees C) and bake for another 30-40 minutes. The top should be a nice toasty brown color and it should still be kind of wobbly in the center but look spongy on top.
Remove from the oven and take the smaller cake pan out of the water pan. Let it cool for 10 minutes. Gently tilt/release the cake out of the pan, remove the side parchment paper strips and let it cool for 15 more minutes on a cooling rack. Remove the bottom parchment circle, and let it cool completely. Slice, serve, and enjoy! P.S It tastes really good with whipped cream!
