Step 1: Preheat your oven to 325°F (160°C). Prepare an 8-inch round springform pan. Line the bottom with parchment paper and lightly grease the sides. Wrap the bottom and sides of the pan with a double layer of heavy-duty aluminum foil to prevent water from seeping in during the water bath.
Step 2: In a large heatproof bowl, combine the softened cream cheese, softened butter, and milk. Place the bowl over a pot of simmering water (double boiler method), ensuring the water doesn’t touch the bottom of the bowl. Whisk continuously until the mixture is completely smooth and melted, with no lumps. Remove from heat and let it cool for 5-10 minutes.
Step 3: While the cream cheese mixture is still warm but not hot, whisk in the egg yolks one at a time until fully incorporated and the mixture is uniform and creamy. Add 1/4 cup (50g) of the granulated sugar and whisk until dissolved.
Step 4: Sift the cake flour and cornstarch together directly into the cream cheese-yolk mixture. Whisk until just combined and smooth. Be careful not to overmix, as this can develop gluten and lead to a tougher cake. If using, stir in the lemon juice.
Step 5: In a separate, very clean, large bowl, beat the egg whites with an electric mixer on medium speed. Gradually add the remaining 1/2 cup (100g) of granulated sugar, increasing the speed to high. Continue beating until the meringue forms soft peaks. It should be glossy and hold its shape but still be soft enough to droop slightly at the tip when the whisk is lifted.
Step 6: Gently fold one-third of the meringue into the cream cheese batter using a spatula to lighten the mixture. Then, carefully fold in the remaining meringue in two additions, using a gentle cutting and folding motion. Be very careful not to deflate the meringue, as this is crucial for the cake’s airy texture.
Step 7: Pour the batter into your prepared springform pan. Gently tap the pan on the counter a few times to release any large air bubbles. Place the springform pan into a larger roasting pan. Pour hot water into the roasting pan until it comes about halfway up the sides of the springform pan (creating a water bath).
Step 8: Carefully transfer the roasting pan with the cheesecake to the preheated oven. Bake for 70-80 minutes, or until the top is golden brown and the cheesecake is set but still slightly jiggly in the center when gently shaken. The internal temperature should be around 170-175°F (77-79°C).
Step 9: Once baked, turn off the oven, crack the door open slightly, and let the cheesecake cool inside the oven for at least 1 hour. This slow cooling process prevents cracking and collapsing. After 1 hour, remove the cheesecake from the oven and the water bath. Let it cool completely on a wire rack.
Step 10: Once cooled to room temperature, cover the cheesecake loosely with plastic wrap and chill in the refrigerator for at least 4 hours, or preferably overnight, before unmolding and serving. This allows the flavors to meld and the texture to fully set.