For Crust: Preheat oven to 325 degrees F.  Line the bottom of a 9-inch springform pan with parchment paper.  Spray the bottom and sides of the pan with nonstick cooking spray.  Set aside.

Combine the graham cracker crumbs, sugar and melted butter in a bowl.  Press into the bottom and up the sides of the prepared pan.   Bake the crust for 10 minutes.  Allow crust to cool, then wrap the outside of the pan with aluminum foil.  This keeps water out of the cheesecake.  Set aside.  Reduce oven to 300 degrees F.

For Cheesecake:. Using a standing or hand=held mixer, beat cream cheese, sugar and flour on low speed until smooth.  Scrape the bottom and sides of the bowl.  Add the sour cream, vanilla and lemon zest.  Mix on low until evenly combined. Add the eggs one at a time on low speed.  Be sure each egg is evenly combined before adding the next.  Scrape the bottom and sides of the bowl.    Pour batter into the cooled crust.  Tap the pan on the countertop to bring any air bubbles in the cheesecake to the surface.

Place the springform pan into a larger baking dish.  Fill the outer pan with enough hot water to go about halfway up the side of the springform pan.  Bake the cheesecake in the hot water bath for 1 hour and 15 minutes.  The center of the cheesecake will be slightly jiggly.

Turn off the oven and allow the cheesecake to stay in the closed oven for an additional 30 minutes.  The cheesecake will continue to cook, and cool at the same time.  Crack the oven for another 30 minutes to let the cheesecake cool slowly.  This process prevents the cheesecake from cracking.  Remove the pans from the oven.  Place the cheesecake in the refrigerator to cool completely as you make the Lemon Curd Topping.

For Lemon Curd Topping:  Combine all ingredients in a double boiler over medium high heat.   Stir constantly until the temperature of the curd reaches 170 to 180 degrees F on a candy thermometer.  When done, the curd will coat the back of a spoon and leave a line when you run a finger through it.   Pour the Lemon Curd over the cheesecake and spread evenly.  Return the cheesecake to the refrigerator to cool completely until firm, about 6 hours.

For Meringue ToppIng:. In a large bowl, or standing mixer bowl, combine sugar, cream of tarter, vanilla and egg whites.  Place over the same double boiler pan used for the lemon curd.   Whisk the mixture constantly until the sugar is dissolved completely and egg whites reach 160 degrees F on a candy thermometer.  Remove from the heat.

Using a standing or hand-held mixer, beat the egg white mixture on medium speed until stiff, glossy peaks form, about 5-7 minutes.  Scoop the meringue onto the top of the cheesecake forming a dome and adding decorative peaks if desired.   Toast the meringue with a kitchen torch or under the oven broiler.

Lemon Meringue Cheesecake is best eaten cold and within 4-5 days.