01 - Preheat the oven to 325°F. Line a 9-inch springform pan with parchment paper, ensuring the bottom and sides are fully covered.
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 together on medium speed until completely smooth and free of lumps.
04 - Add the eggs one at a time, mixing on low speed after each addition until just incorporated. Fold in the sour cream, flour, vanilla extract, and lemon zest, mixing until the batter is homogeneous. Avoid overmixing.
05 - Pour the filling over the cooled crust. Gently tap the pan on the countertop several times to release any trapped air bubbles.
06 - 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.
07 - Turn off the oven and crack the door open. Allow the cheesecake to cool gradually inside the oven for 1 hour to prevent cracking.
08 - If using the topping, whisk together the sour cream, powdered sugar, and vanilla extract until smooth. Spread evenly over the cooled cheesecake surface.
09 - Refrigerate the cheesecake for at least 6 hours, preferably overnight. Before serving, run a thin knife around the pan edges, release the springform ring, slice into portions, and serve chilled.