Grease 9″ (23-cm) round baking pan, then line with parchment paper. (Reminder: The parchment paper should be 1″ higher than the pan.)
Preheat oven to 160°C/320°F. (Reminder: Preheat to 160°C/320°F but bake at 150°C/300°F.)
Combine Cheddar cheese, butter and milk in stainless steel bowl. Sit the bowl in hot simmering water, cook until melted.
Sieve in plain flour and cornstarch, mix until blended. Add in lemon juice and egg yolks, mix until smooth.
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 3 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.
Put a piece of cloth in a larger pan, fill with hot water for water bath (about 1″ high). Put baking pan with batter into the larger pan.
Bake at 150°C/300°F for 50 minutes, then reduce to 140°C/285°F and bake for 60-70 minutes, until fully cooked (wooden stick inserted in the center of the cake comes out clean) and the top is nicely browned.
Remove the water bath, switch off the oven, let the Cheddar Cheese Cotton Cheesecake cool in the oven for 40 minutes with the door slightly ajar.
After cooling in the oven for 40 minutes, unmould the cake and cool completely on wire rack (at least 6″ from countertop).
When completely cooled, keep Cheddar Cotton Cheesecake refrigerated for 4-5 hours until chilled before slicing.