Reduce the oven to 300°F. Prepare the water bath. Place a folded towel in the bottom of a large roasting pan or baking dish (make sure the springform pan fits in there comfortably with space on all sides).
Heat 6 cups of water to boiling. Turn off the heat and let it sit while you prepare the cheesecake.
In a large mixing bowl or the bowl of a stand mixer, add the sugar and lemon zest and beat until combined, about 1 minute. The sugar should be quite fragrant and smell like lemon.
¾ cup granulated white sugar, 2 tablespoons lemon zest
Add the cream cheese to the bowl and beat on medium speed and light and fluffy, about 5 to 6 minutes. Keep in mind that you want to beat the cream cheese but not add air into the mixture.
24 ounces cream cheese
Add the sour cream (or Greek yogurt), lemon juice and lemon extract and beat until fully combined, another 2 to 3 minutes.
1 cup sour cream, ¼ cup lemon juice, 1 to 2 teaspoons lemon extract
Add in the eggs, one a time, beating on low speed, just until combined. Do not overbeat.
4 large eggs
Wrap the springform pan in 2 layers of heavy duty aluminum foil to prevent water from getting in. I like to use the wide aluminum for extra protection.
Transfer the cheesecake mixture into the cooled crust and use an offset spatula to create an even layer. Tap the pan - gently - several times on the counter to pop any air bubbles.
Carefully place the springform pan on the folded towel in the roasting pan and place it in the oven.
Once the pan is in the oven, carefully pour the hot water into the baking pan, away from the cheesecake, until it reaches about the middle of the springform pan, at least 1 to 2 inches. (This water bath ensures that the cheesecake bakes evenly and helps reduce the possibility of cracking.)
Bake for 75 to 90 minutes or until the cheesecake has just a slight jiggle in the middle when the springform pan is moved. Start checking every three minutes after 75 minutes has passed.
Turn off the oven (leave the door closed) and leave the cheesecake in the oven for 30 minutes. It will continue to cook while the oven cools.
Crack the oven door and let the cheesecake cool for another 40 to 45 minutes in the oven. Make sure the pan has cooled enough that it can be comfortably handled before removing from the oven.
Transfer the cheesecake to a cooling rack and let it set at room temperature for 30 to 45 minutes. Gently spread the lemon curd over the top of the cheesecake leaving ¼ to ½ inch of space around the edges free of curd.
½ cup lemon curd
Cover with plastic wrap and chill in the refrigerator overnight (or for a minimum of 4 hours).