Line the base of an 8-inch springform pan with parchment paper and grease with oil or butter. Since we're baking this cheesecake in a water bath, wrap your pan with heavy-duty aluminum foil to avoid seepage later.
Sift cake flour, cornstarch and salt. Set aside.
Melt cream cheese in a double boiler then add butter and milk. Mix well until combined (see notes).
Remove from heat then add in the flour mixture and lemon juice, and stir until combined. This cream cheese mixture needs to cool so while waiting, preheat your oven to 325F and work on your egg whites.
Using a stand mixer with the whisk attachment, whisk the egg whites with the cream of tartar until soft peaks form (you can also use an electric mixer or even whisk the egg whites by hand - just think of it as a mini-workout).
Gradually add the sugar until stiff peaks form.
At this point your cream cheese mixture should be cool so you can mix in the the egg yolks. Stir until well combined. To ensure there are no lumps, sift and transfer this mixture into another bowl.
Go back to your egg whites and gently fold a third into your cream cheese mixture. Add another third and fold. Then add in the rest of your egg whites and fold until just combined.
Pour your batter into your springform pan and lightly drop on your counter a few times to release any air bubbles.
Put the springform pan in a roasting pan with about an inch of cold water.
Bake for 45 minutes or until set and golden brown.
Turn off the oven but to avoid cracks, leave the cheesecake in the oven with the door slightly open for another 5 minutes.
Then take the pan out and cool completely. Carefully remove the cake from the pan and chill in the fridge overnight to allow it to set.
Leave on the counter for about 10 minutes before serving.
Notes
I don't like double boilers so I sometimes just use the "Soften" feature of our microwave to melt the cream cheese. I don't melt it all the way - just until the point where I can finish the melting process myself by mixing the cream cheese with a spatula. I then add the butter and milk, pop it in the microwave for a quick 10 seconds and then mix again.