Preheat oven to 320°F (160°C). Grease 8-inch (20cm) round cake pan with butter, line bottom and sides with parchment paper. Grease the parchment as well. If using springform pan wrap the pan tightly with aluminum foil.
Melt cream cheese, butter, milk and ¼ cup (50g) sugar over a double boiler.
Remove the mixture from heat. Add egg yolks and stir until combined. Sift flour and cornstarch and stir until incorporated. Add lemon zest and lemon juice and stir until combined.
Whisk egg whites at low speed until foamy, gradually add the sugar while continuing to beat until stiff peaks form.
Using a whisk, mix in 1/3 of egg whites into the cream cheese mixture until incorporated. Then gently fold in another 1/3 into the mixture, then gently fold the last 1/3.
Pour the batter into the cake pan and tap the pan on the counter to release air bubbles.
Place pan into a deep roasting pan (larger in size). Pour boiling water into roasting pan so that water comes halfway up the sides of the springform pan.
Bake for 20 minutes, then reduce the heat to 285°F (140°C), and bake for another 30-35 minutes.
Turn off the oven and leave cake in the closed oven for another 30 minutes. Remove the cake from the oven and let cool until ready to serve.
Notes and tips:
Use room temperature egg whites.
For extra fluffy cheesecake use 1 or 2 more egg whites.
For topping you can dust the cake with powdered sugar.