Grease and line 9-inch/23-cm round baking pan with parchment paper.
Preheat oven to 160°C/320°F.
Combine cream cheese, butter, salt and sugar in stainless steel bowl, heat over hot simmering water, mix until smooth. Add in milk, mix until combined.
Combine plain flour and Matcha powder, sift through and mix well. Sift again into cheese batter, mix until smooth. Add in egg yolks gradually, mix until combined.
In a clean mixing bowl, whisk egg whites over low speed until foamy. Add in lemon juice, whisk until small bubbles are formed. Add in sugar gradually, whisk until soft peaks (meringue is shiny with arch shape).
Add meringue into cheese batter in 4 batches, mix gently with hand whisk. Fold gently until well mixed with spatula. Tap mixing bowl a few times on countertop to burst large bubbles.
Pour the batter into lined baking pan, tap baking pan a few times to break large bubbles.
Line a piece of cloth in 10-inch/25-cm square baking pan, fill with plain water for water bath (about 1″ high). Put in baking pan with batter. (Reminder: I prefer to use plain water for water bath as the cake tends to crack if hot water is used.)
Bake at 150°C/300°F for 40 minutes, then at 140°C/285°F for 1 hour 20 minutes, until fully cooked.
Remove the water bath, leave oven door slightly ajar, switch off the oven, let the Matcha Cotton Cheesecake cool in the oven for 40-45 minutes (to minimise shrinkage).
Unmould the Matcha Light Cheesecake and cool completely on wire rack (at least 6″ from countertop).