01 - Preheat oven to 325°F. Line a 9-inch springform pan with parchment paper, pressing it flat against the bottom.
02 - Combine graham cracker crumbs, 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 softened cream cheese and sugar with an electric mixer on medium speed until completely smooth and free of lumps. Add eggs one at a time, beating briefly after each addition. Fold in sour cream, flour, vanilla extract, and lemon zest until just combined — do not overmix.
04 - Pour the filling over the partially cooled crust. Gently tap the pan on the counter several times to release any trapped air bubbles.
05 - Bake on the center rack for 50 to 60 minutes, until the edges are set and the center still has a slight jiggle when gently shaken.
06 - Turn off the oven and crack the door open. Let the cheesecake rest inside the cooling oven for 1 hour to prevent cracks from forming.
07 - Whisk together sour cream, powdered sugar, and vanilla extract until smooth. Spread evenly over the cooled cheesecake surface.
08 - Refrigerate the cheesecake for at least 6 hours, preferably overnight. Run a thin knife around the pan edge, release the springform ring, slice into wedges, and serve chilled.