Turn down the heat to 275°F.
In bowl: beat/mix cream cheese until smooth. Use a spatula to scrap the sides of the cheesecake batter to center of the bowl. Add sugar and beat until smooth. Add sour cream, vanilla extract, lemon juice, salt and beat until smooth. Use a spatula to scrap the sides of the cheesecake batter to center of the bowl.
Add cornstarch (make sure to sift it) and mix everything together until smooth.
Beat on low speed (to avoid air bubbles). In increments- add 1 egg at a time and whip until smooth. DO NOT SKIP THIS PART. Tip: have 4 separate bowls with each egg ready to use. Use a spatula to transfer the batter to the springform.
Water Bath- Place the cheesecake in the center of the roasting/lasagna pan. Carefully add boiling hot water into the bottom of the pan ~ up to halfway full. Do not get any water in the cheesecake.
Carefully place the pan in the center of the preheat oven. Cook for 2 hours at 275°F. Then, turn off the oven and leave the pan with cheesecake for 1 hour longer unopened (do not open the oven door). Then, open the oven door approx. half way, leaving the cheesecake undisturbed for 1 more hour. Lastly, remove cheesecake from the oven.
Slowly and carefully remove the aluminum foil from the pan. Place the cheesecake on the counter and let set at room temperature for 2-3 hours. Use a knife to loosen the cheesecake from the springform. Refrigerate for 8 hours or overnight (recommend: do not cover the cheesecake while in the refrigerator).