Preheat oven to 320 degrees F (160 degrees C). Grease a small loaf pan.
Beat sugar and egg whites together in a bowl using an electric mixer until stiff peaks form. Add egg yolk and mix well. Stir grapeseed oil, honey, and milk into egg mixture.
Sift flour and green tea powder 2 times into a bowl; mix into egg mixture. Pour batter into prepared pan.
Bake in the preheated oven until a toothpick inserted in the center comes out clean, about 50 minutes.
