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 on medium speed, beat the softened cream cheese and sugar together until completely smooth and free of lumps, scraping down the bowl as needed.
04 - Add the eggs one at a time, beating briefly after each addition. Fold in the sour cream, flour, vanilla extract, and lemon zest, mixing until just combined. Do not overmix.
05 - Pour the filling over the partially cooled crust. Gently tap the pan on the countertop several times to release any trapped air bubbles.
06 - Bake for 50 to 60 minutes, until the edges are set and the center still has a slight jiggle when gently shaken.
07 - Turn off the oven, crack the door open slightly, and allow the cheesecake to cool inside for 1 hour. This gradual cooling helps prevent cracks on the surface.
08 - If using the topping, whisk together the sour cream, powdered sugar, and vanilla extract until smooth. Spread evenly over the cooled cheesecake.
09 - Refrigerate the cheesecake for at least 6 hours, preferably overnight. Before serving, run a thin knife around the edge of the pan and release the springform ring. Slice with a clean, warm knife for clean portions.