Preheat the oven to 325°F (160°C). You will need at least 2.5-in (6cm) deep 8-in (20sm) springform pan. Cut 3.5-inch (9cm)-wide long strip and 8-inch (20cm) round circle of parchment paper. Line the sides and the bottom of the springform pan with the prepared parchment paper. Set aside.
Zest and juice the lemon. You should get about 1 teaspoon of lemon zest and 2 tablespoons of lemon juice.
Separate the egg whites and yolks. Set aside.
In a mixing bowl with paddle attachment, or using a handheld electric mixer, beat the cream cheese until smooth and fluffy, about 2 minute. Add condensed milk and beat for another minute. Then add the egg yolks and lemon zest with lemon juice. Continue to beat until well combined, 2-3 minutes.
In a separate bowl, beat the egg whites until hard peaks form. Make sure the bowl and the beaters are squeaky clean and free of grease. (Tip: Egg whites at room temperature are easier to beat and reach hard peaks faster.)
Fold in half of the whipped egg whites into the cream cheese mixture. Then add the remaining egg whites and gently fold until well-combined and no white streaks are visible.
Transfer the batter into the prepared pan and tap on the counter a few times to release any air bubbles. Place an empty baking sheet on lower rack of the oven and pour about 2 cups of boiling water. Put the cake pan on the middle rack above the rack with water bath. Bake for 45 minutes.
Turn off the oven and cool the cake in the oven for 30-40 minutes. Remove the sides of the springform pan and gently peel off the parchment paper from the sides. Cool completely on the counter, then refrigerate until ready to serve.
Before serving, when the cake is chilled and set, gently remove the parchment paper from the bottom and place the cake on a platter. Dust with powdered sugar, if desired. Store the cake in the fridge, covered, for up to 3 days.
For step-by-step photos and additional notes, read the post above.