01 - Preheat oven to 325°F. Line a 9-inch springform pan with parchment paper, pressing it flat against the bottom.
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 - Beat the softened cream cheese and sugar with an electric mixer on medium speed until completely smooth and free of lumps. 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.
04 - Pour the filling over the cooled crust, spreading evenly. Gently tap the pan on the counter several times to release trapped air bubbles. Bake for 50 to 60 minutes, until the edges are set and the center retains a slight jiggle.
05 - Turn off the oven, crack the door open slightly, and let the cheesecake remain inside for 1 hour. This gradual cooling helps prevent cracking.
06 - Whisk together the sour cream, powdered sugar, and vanilla extract until smooth. Spread the mixture evenly over the cooled cheesecake surface if desired.
07 - Refrigerate the cheesecake for at least 6 hours, preferably overnight, until fully set and chilled through.
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 for clean edges and serve.