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 (peaks should bend slightly at the tips). Do not over-beat.

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

Add remaining egg whites in two additions, folding gently from bottom to top while rotating the bowl. Fold just until no white streaks remain, being careful not to deflate the batter.

Pour batter into prepared pan and tap gently on counter 2-3 times to release air bubbles.

Place cake pan inside larger roasting pan. Carefully pour hot water into outer pan until it reaches halfway up the sides of the cake pan.

Bake for 50-60 minutes, until top is lightly golden and center jiggles slightly when gently shaken. The cake should be set but not completely firm.

Turn off oven, crack door open about 4 inches, and let cake cool inside for 30 minutes.

Remove from oven and water bath. Let cool to room temperature on wire rack, about 1 hour.

Cover and refrigerate for at least 3 hours or overnight before serving.

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