Prepare the pan: Preheat the oven to 320°F (160°C). Grease and line an 8-inch round cake pan with parchment paper, and wrap the exterior with aluminum foil to prevent water leakage during the water bath.

1. Melt the cream cheese, butter, and white chocolate: Melt the cream cheese, butter, and chopped white chocolate over a double boiler or in the microwave. Stir in milk and matcha powder until smooth.
2. Prepare the egg yolk mixture: Whisk egg yolks and half of the sugar (50g) until pale and thickened. Add to the cream cheese mixture and whisk until fully combined.
3. Combine the dry ingredients: Sift together flour, cornstarch, and salt, then fold into the cream cheese mixture until smooth.
4. Whisk the egg whites: Beat egg whites with cream of tartar until frothy. Gradually add the remaining sugar (50g) and continue beating until stiff peaks form.
5. Fold the mixtures together: Gently fold the egg whites into the matcha mixture in three additions, being careful not to deflate the batter.
6. Bake the cheesecake: Pour the batter into the prepared pan, smooth the top. Place the pan in a larger roasting pan and pour hot water into the outer pan to create a water bath. Bake for 50-60 minutes, or until the top is golden and a toothpick comes out clean.
7. Cool and chill: Turn off the oven and let the cheesecake cool inside with the door ajar for 1 hour. Then refrigerate for at least 4 hours or overnight to set.
8. Serve: Before serving, dust with powdered sugar and matcha powder for an elegant finish.