Preheat oven to 320°F (160°C). Line a 7-inch round springform pan with parchment paper on bottom and sides. Prepare a larger roasting pan for water bath.

In a medium bowl, beat softened cream cheese until smooth and creamy with no lumps, about 2 minutes.

Add egg yolks, milk, vanilla extract, lemon juice, and cornstarch to cream cheese. Mix on medium speed until fully combined and silky smooth. Set aside.

In a separate large clean bowl, beat egg whites with cream of tartar and salt using an electric mixer on medium speed until foamy.

Gradually add monk fruit sweetener (or sugar) while continuing to beat. Increase speed to medium-high and whip until soft to medium peaks form.

Gently fold one-third of the whipped egg whites into the cream cheese mixture using a spatula, stirring in circular motions.

Add remaining egg whites in two additions, folding gently from bottom to top until no white streaks remain.

Pour batter into prepared pan and tap gently on counter. Place pan in a larger roasting pan filled halfway with hot water. Bake for 50-60 minutes.

Turn off oven, crack door, and let cake cool inside for 30 minutes. Remove cake and cool to room temperature for about 1 hour. Refrigerate for at least 3 hours or overnight.

Run a thin knife around edges before releasing springform pan. Slice with a clean knife, wiping between cuts.