In a medium saucepan over medium-low heat, whisk together eggs, sugar, lemon juice, lemon zest, and salt.

Continue whisking constantly until the mixture thickens, about 8–10 minutes. It should coat the back of a spoon.

Remove from heat and stir in the butter until melted, then pour through a fine mesh strainer into a clean bowl.

Press plastic wrap onto the surface and refrigerate until cool.

Preheat the oven to 325°F (163°C). Wrap the springform pan with aluminum foil.

In a mixing bowl, combine graham cracker crumbs, sugar, melted butter, and a pinch of salt. Mix until combined.

Press into the bottom of the foil-wrapped springform pan and slightly up the sides.

Bake the crust in the oven for 10 minutes. Set aside to cool.

In a stand mixer, beat cream cheese on medium speed until smooth, about 3 minutes.

Add sour cream and mix until combined.

Gently fold in cooled lemon curd until the mixture is uniform.

Pour the cheesecake filling into the cooled crust. Tap to remove air bubbles.

Place the springform pan in a larger roasting pan, and add hot water halfway up the sides of the springform pan.

Bake at 325°F for 60 to 70 minutes, until the outer edges are set but the center has a slight jiggle.

Turn off the oven and let the cheesecake cool inside with the door cracked for 1 hour, then cool at room temperature for another hour before refrigerating overnight.

Run a knife around the edge, release the sides of the springform pan, slice, and serve. Top with lemon curd or whipped cream if desired.