Prepare the Lemon Curd:
In a small saucepan, whisk together the lemon juice, lemon zest, sugar, and egg yolks.
Cook over medium heat, stirring constantly, until the mixture thickens enough to coat the back of a spoon (about 5–7 minutes).
Remove from heat and stir in the butter until fully melted.
Strain the curd through a fine-mesh sieve to remove any lumps. Let it cool to room temperature.
Make the Crust:
Preheat your oven to 350°F (175°C). Line a 9x9-inch baking pan with parchment paper, leaving an overhang for easy removal.
In a bowl, combine the graham cracker crumbs, sugar, and melted butter.
Press the mixture evenly into the bottom of the prepared pan. Bake for 8–10 minutes, then let cool.
Prepare the Cheesecake Filling:
In a large mixing bowl, beat the cream cheese and sugar with an electric mixer until smooth and creamy.
Add the eggs one at a time, mixing well after each addition. Stir in the sour cream and vanilla extract.
Pour the cheesecake filling over the cooled crust, spreading it evenly with a rubber spatula.
Add the Lemon Swirl:
Drop spoonfuls of the cooled lemon curd over the cheesecake filling.
Use a skewer or knife to swirl the curd into the filling, creating a marbled effect.
Bake:
Bake the cheesecake bars for 30–35 minutes, or until the center is just set.
Let them cool to room temperature, then refrigerate for at least 4 hours or overnight.
Serve:
Once chilled, lift the cheesecake out of the pan using the parchment paper overhang.
Slice into bars and serve.