Preheat the oven to 325°F.
In a medium sized saucepan, melt the cream cheese, butter and milk over medium-low heat. Stir often to ensure the mixture doesn't burn.
Beat the egg yolks in a separate small bowl.
Remove the cream cheese mixture from the heat and pour a very small amount in the bowl (about 3 tablespoons) with the egg yolks, whisking continuously, to temper the egg yolks.
Pour another small amount in (about 3 tablespoons) while whisking continuously.
Pour the cream cheese mixture in a bowl and whisk the tempered egg yolk and lemon juice in. Be sure to whisk continuously to avoid lumps.
Combine the flour, cornstarch and salt in a small bowl and mix to combine.
Gently fold the flour mixture into the cream cheese mixture, being careful not to over-mix.
In a separate bowl, use a mixer (either a hand mixer or a counter top mixer), to beat the egg whites until the become frothy and bubbly, about 2 minutes.
Add the cream of tartar and beat for 1 minute.
Add the sugar, ⅛ cup at a time, beating until the mixture is smooth (not grainy), between each ⅛ cup.
Continue beating the mixture until soft to medium peaks form.
Fold ⅓ of the egg whites mixture into the cream mixture, being careful not to over-mix and deflate the egg whites.
Fold another ⅓ of the egg whites in, then the last ⅓ of the egg whites, always being careful to fold gently and not over-mix.
Wrap foil securely around the bottom 2 inches of a 8-9" greased springform pan.
Pour the mixture into the springform pan.
Fill a large baking dish or pan with 1 inch of water. Place the springform pan into the baking dish.
Bake on the bottom rack of the oven for 60-70 minutes, or until a toothpick comes out clean.
Turn off the heat and leave the cheesecake in the oven with the oven door cracked open for an hour.
Remove from the oven and let cool fully on the counter. Remove it from the springform pan and refrigerate for at least 3 hours, or overnight.
Slice and serve with fresh berries, lemon curd, whipped cream and/or powdered sugar.