01 - Preheat the oven to 325°F. Line a 9-inch springform pan with parchment paper on the bottom and lightly grease the sides.
02 - Combine the crushed graham crackers, sugar, and melted butter in a bowl until the mixture resembles wet sand. Press firmly and evenly into the bottom of the prepared pan. Bake for 10 minutes, then set aside to cool slightly.
03 - Using an electric mixer, beat the softened cream cheese and sugar on medium speed until completely smooth and free of lumps. Add the eggs one at a time, mixing well after each addition. Blend in the sour cream, flour, vanilla extract, and lemon zest until just combined — do not overmix.
04 - Pour the filling over the cooled crust. Gently tap the pan on the counter several times to release any trapped air bubbles. Bake for 50 to 60 minutes, until the edges are set and the center still has a slight jiggle.
05 - Turn off the oven, crack the door open slightly, and let the cheesecake rest inside for 1 hour. This slow cooling helps prevent cracks from forming on the surface.
06 - If using the topping, whisk together the sour cream, powdered sugar, and vanilla extract until smooth. Spread the mixture evenly over the cooled cheesecake.
07 - Refrigerate the cheesecake for at least 6 hours, preferably overnight, to allow it to fully set and develop its signature creamy texture.
08 - Run a thin knife around the edge of the pan to loosen the cheesecake, then release the springform ring. Slice with a clean, warm knife and serve.