01 - Preheat the oven to 320°F. Line the bottom and sides of an 8-inch round cake pan with parchment paper. Wrap the outside of the pan with aluminum foil to prevent water from seeping in during baking.
02 - In a heatproof bowl over a pot of simmering water, melt the cream cheese, butter, and milk. Stir until smooth, then remove from heat and let cool slightly.
03 - Sift the cake flour, cornstarch, and salt together. Add to the cream cheese mixture and whisk until fully incorporated.
04 - Add the egg yolks, lemon juice, vanilla extract, and lemon zest (if using) to the mixture. Mix until smooth and set aside.
05 - In a clean bowl, beat the egg whites with an electric mixer on medium speed until foamy. Gradually add 5 tbsp sugar in three parts, beating until stiff, glossy peaks form.
06 - Gently fold one-third of the meringue into the cream cheese batter to lighten the mixture. Carefully fold in the remaining meringue in two additions, taking care not to deflate the batter.
07 - Pour the batter into the prepared pan. Tap the pan gently on the counter to release air bubbles.
08 - Place the cake pan into a larger roasting pan. Add hot water to the roasting pan until it reaches halfway up the sides of the cake pan.
09 - Bake for 60–70 minutes, or until the cake is golden, set, and a skewer inserted into the center comes out clean.
10 - Turn off the oven and leave the cheesecake inside with the door ajar for 15 minutes to prevent cracking.
11 - Remove from the oven and let cool completely in the pan before unmolding. Chill in the refrigerator for at least 2 hours before serving.