Using a nonstick 8-inch springform cake pan, line the bottom with baking paper and wrap the outside of cake pan with foil to prevent leakage.
Preheat the oven to 160°C - 320°F.
In a mixing bowl, whisk egg yolks and egg until light and fluffy using medium speed. It will take abour 3-5 minutes.
Lower the speed and add the oil slowly and once the oil is well blended, add the milk. Continue to mix for few seconds until well combined.
Add the flour and matcha powder and mix for few seconds. Scrape the sides and the bottom of the bowl to make sure everything is well combined. Set it aside.
Using another mixing bowl, add the egg white and turn on the mixer on low speed. Once the egg whites become foamy, add in cream of tartar. Increase the speed of the mixer and continue to whip until soft peak.
Once the egg whites are soft peak and cloudy, slowly add in the sugar while the mixer is running and continue to whip until stiff peak.
Fold 1/3 of egg white mixture into the egg yolk batter. Continue to add the next 3rd and repeat until all the egg white mixture is finished.
Transfer the cake batter into the prepared cake pan. Tap the cake pan few times to remove trapped air bubbles.
Fill the baking tray with 1 3/4 cups hot water.
Bake in the oven for 70 minutes.
Once done, remove the cake pan and let it cool on a cooling rack for 1 hour or until the cake has separated from cake pan.
Remove the cake from the cake pan and dust the top with powdered sugar and matcha green tea powder
Don't add sugar before whipping the egg whites. It's hard to achieve stiff peak stage when you add the sugar at the early stage. Slowly add the sugar when the whites have formed soft peaks.
Use caster sugar when whipping egg whites because it dissolves faster and easily.
3. Fold the egg white mixture gently and slowly to keep its shape without deflating the air of the light ingredients.4. This sponge cake recipe is like a soufflé. It will deflate after few minutes once it was removed from the oven. When your baking a soufflé in the oven, hot air gets trapped inside and once it has been taken out from the oven, hot air escapes causing it to deflate.