Prep: Preheat oven to 325°F (160°C). Line a 9x9-inch (22x22cm) square pan or 20x25cm rectangular pan with parchment paper.
Make the crust: In a food processor, process the graham crackers into fine crumbs. Add melted butter and pulse until combined. Press firmly into the bottom of the prepared pan. Bake for 7–10 minutes. Let cool slightly.
Make the filling: In a large bowl, beat cream cheese, sugar, vanilla extract, lemon zest, and lemon juice until smooth. Add sour cream and mix until combined. Add eggs one at a time, mixing just until incorporated after each addition. Do not overmix.
Pour the filling over the crust and smooth the top. Bake for 35–40 minutes, or until the edges are set and the center is slightly jiggly. Let cool at room temperature for 1 hour, then refrigerate for at least 4 hours or overnight.
Make the lemon curd topping: In a saucepan, whisk sugar, cornstarch, and salt. Add water and lemon juice and whisk until smooth. Cook over medium heat, stirring constantly, until thickened and boiling. In a separate bowl, whisk egg yolks. Gradually whisk in about ½ cup of the hot mixture, then pour back into the saucepan. Cook for 1–2 minutes more, stirring constantly, until thick and glossy. Remove from heat and stir in butter and lemon zest.
Let the topping cool slightly, then pour over the chilled cheesecake and spread evenly. Refrigerate for at least 1 hour.
Cut and serve: Lift the cheesecake out of the pan, trim the edges if desired, cut into bars, and serve.
Video
Notes
Bake until slightly jiggly: The center should still wobble slightly when removed from the oven. The cheesecake will continue to set as it cools.
Chill completely before slicing: For clean bars and the best texture, refrigerate overnight if possible.
For neat slices: Wipe the knife clean between each cut.
Crust options: Graham crackers, digestive biscuits, Petit Beurre, or vanilla biscuits all work well.
Storage: Store covered in the refrigerator for up to 5 days.
Freezing: Freeze without the topping for up to 2 months. Thaw overnight in the refrigerator before serving.
Optional garnish: Top with lemon slices, whipped cream, or fresh mint leaves before serving.