Step 1: Prepare the Crust

1. Preheat your oven to 325°F (160°C). Grease a 9-inch springform pan and line the bottom with parchment paper.
2. In a medium bowl, combine the graham cracker crumbs, sugar, and melted butter. Mix until evenly moistened.
3. Press the mixture firmly into the bottom of the prepared pan to form an even crust. Use the back of a measuring cup for a smooth finish.
4. Bake the crust for 10 minutes, then set aside to cool while preparing the filling.

Step 2: Make the Raspberry Swirl

1. In a small saucepan, combine the raspberries, sugar, lemon juice, cornstarch, and water.
2. Cook over medium heat, stirring frequently, until the mixture thickens and the raspberries break down (about 5 minutes).
3. Strain the mixture through a fine mesh sieve to remove the seeds, pressing down with a spoon to extract as much liquid as possible. Set aside to cool.

Step 3: Prepare the Filling

1. In a large mixing bowl, beat the cream cheese and sugar together with an electric mixer until smooth and creamy.
2. Add the sour cream, flour, lemon zest, and lemon juice, mixing until fully incorporated.
3. Add the eggs one at a time, beating on low speed after each addition to avoid overmixing. Stir in the vanilla extract.

Step 4: Assemble the Cheesecake

1. Pour the cheesecake filling over the cooled crust, spreading it evenly.
2. Drop spoonfuls of the raspberry sauce onto the filling. Use a skewer or toothpick to gently swirl the sauce into the cheesecake for a marbled effect.
3. Place the springform pan on a baking sheet to catch any drips.

Step 5: Bake the Cheesecake

1. Bake the cheesecake for 60–70 minutes, or until the edges are set and the center has a slight jiggle.
2. Turn off the oven and crack the door open. Allow the cheesecake to cool in the oven for 1 hour to prevent cracking.

Step 6: Chill and Serve

1. Once cooled, cover the cheesecake with plastic wrap and refrigerate for at least 4 hours or overnight.
2. Carefully remove the springform pan and transfer the cheesecake to a serving plate.
3. Slice and serve chilled, garnished with fresh raspberries or whipped cream if desired.