Preheat your oven to 300°F (150°C) and prepare a 6-inch round baking pan by lining it with parchment paper.

In a double boiler, combine the unsalted butter, cream cheese, and milk. Stir until well blended and reaches 130°F (55°C).

Remove melted mixture from heat, whisk in egg yolks and vanilla extract. Sift in cake flour and cornstarch, mixing until smooth.

In a separate bowl, beat egg whites with lemon juice until frothy. Gradually add sugar and whip to medium-soft peaks.

Gently fold one-third of the meringue into the batter, then fold in the remaining meringue until just combined.

Pour batter into prepared pan, place in a larger tray filled with boiling water. Bake at 300°F (150°C) for 30 minutes, then reduce to 230°F (110°C) for 30 more minutes, finally raise to 275°F (135°C) for 13-15 minutes.

Turn off the oven and leave the cheesecake inside for 15 minutes with the door ajar to cool gradually.

Remove the cheesecake from the water bath, allow it to cool for another 15 minutes before transferring to a wire rack.

Cool completely before gently removing from the pan and dusting with powdered sugar for an elegant finish.