Place the softened cream cheese, sugar, salt, and corn starch (or flour) in the bowl of your mixer fitted with the paddle attachment (alternatively, you can use a hand-held electric mixer and a large bowl). On medium-low speed (NOT high), cream the ingredients together until creamy and silky and no lumps of cream cheese remain. Use a spatula to scrape down the edges of the bowl making sure everything is well incorporated.
Add the lemon zest, lemon juice, and vanilla to the cream cheese and mix thoroughly.
Add the sour cream and beat on medium until well combined.
Add the eggs to the batter, one at a time, waiting until the first egg is just barely incorporated before adding the next one. Mix fully.
Remove the bowl from the mixer stand and use a spatula to scrape down the sides and bottom of the bowl. Stir the batter by hand a few times, making sure everything is as incorporated as possible.
Pour the batter over the cooled crust.
Transfer the lemon cheesecake to a large roast pan (or baking dish big enough to hold it).
Boil a kettle of water and fill the roasting pan with boiling water, to about an inch (or lower) below the top rim of the springform pan. Be very careful not to splash any water on the cheesecake.Carefully transfer the roasting pan to the preheated oven.
Bake the cheesecake in the water bath for 40-45 minutes. Do NOT overbake. Your perfectly cooked cheesecake will still have a good amount of jiggle in the center when you gently shake the pan, while the outer inch will be more firm.
Turn the oven off, prop the oven door open about an inch or 2, and leave the cheesecake in the oven for an additional hour to slowly start to cool.
After an hour of cooling in the oven, remove the cheesecake from the oven and from the water bath. Run a sharp knife around the edge of the cheesecake to make sure it’s not sticking to the sides (which can cause it to crack while cooling). Take the tinfoil off your pan and allow the cheesecake to completely cool on a cooling rack.
Chill the cheesecake, uncovered, in the fridge for a least 4 hours, but ideally, overnight. DO NOT SKIP THIS STEP! This step is extremely important for achieving the perfect cheesecake texture; velvety, creamy, and smooth.
When you’re ready to serve your cheesecake, remove the outer ring of the springform pan and oh so carefully, transfer the cheesecake from the springform bottom to a serving platter.Spread a generous layer of lemon curd over the top of the cheesecake, or don't - the cheesecake is still incredible without it!