With an electric mixer, beat the egg yolks and sugar for several minutes until the mixture becomes thick and pale. Add the citrus juice and mix until blended.
Pour the mixture into a heavy-bottomed stainless steel saucepan. Add butter, salt, and lemon zest. Cook the mixture, whisking constantly, until thickened (about 10 minutes) and coats the back of a metal spoon. Do not let it boil.
Transfer to a small bowl; cool 10 minutes. Refrigerate, covered, until cold.
For the crust
Preheat the oven to 350 degrees Fahrenheit.
In a small bowl, mix the graham cracker crumbs with the melted butter together until evenly moistened. Press the crumb mixture onto the bottom of a 9-inch springform pan. Bake the crust until golden brown, about 10 to 12 minutes.
Cool the pan on a rack for 15 minutes.
For the cheesecake filling
In the bowl of a standing mixer fitted with the paddle attachment, or with a hand-held mixer, beat the cream cheese on medium speed until smooth. Gradually add the sugar and beat until light and fluffy, scraping down the sides of the bowl and beaters as needed.
Beat in the sour cream. Add the eggs, one at a time, beating well after each addition. Stir in the lime juice, zest, and salt; mix until just combined. Stir in the cornstarch.
Assemble and bake
Preheat oven to 350 degrees Fahrenheit.
Pour half of the batter into the prepared pan. Spread 6 tablespoons of lime curd evenly over the top, and then carefully spread the remaining cheesecake batter over the curd (Refrigerate the rest of the curd to use before serving).
Wrap outside of the pan in a double layer of foil, covering the underside and extending all the way to the top. Place the wrapped pan in a large roasting pan and add 2 inches of hot water (or about halfway up the sides of the cheesecake pan).
Bake until the top of the cheesecake is lightly browned but the center still jiggles slightly, about 50 minutes. Remove the aluminum foil and run a thin knife or offset spatula around the edges to release the edges from the pan (prevents it from being torn open).
Allow the cake to completely cool on a rack, then cover with plastic wrap and refrigerate overnight or at least 4 hours before serving.
Before serving, open the springform pan and remove the ring. Distribute the rest of the lime curd evenly on the top of the cake. Cut the cheesecake into wedges and serve with whipped cream if desired.
Replace sugar with a sugar substitute that measures cup for cup, like Swerve.
Do not use an aluminum saucepan for cooking the curd, as it would react with the juice and yolk.
Nutrition information is approximate and meant as a guideline only.