01 - Preheat the oven to 325°F (160°C). Line the bottom of a 9-inch springform pan with parchment paper, ensuring it lies flat against the base.
02 - Combine the graham cracker crumbs, melted butter, and granulated sugar in a bowl, mixing until the texture resembles wet sand. Press the mixture firmly and evenly across the bottom of the prepared pan. Bake for 10 minutes, then set aside to cool completely.
03 - In a large mixing bowl, beat the softened cream cheese with an electric mixer until completely smooth and free of lumps. Gradually add the granulated sugar, continuing to mix until fully incorporated.
04 - Add the eggs one at a time, beating well after each addition. Blend in the sour cream, vanilla extract, all-purpose flour, and lemon juice. Mix until just combined—avoid overmixing to prevent air bubbles.
05 - Pour the filling onto the cooled crust and smooth the surface with a spatula. Bake for 45 minutes, or until the edges are set but the center still has a slight wobble. Turn off the oven, crack the door open, and let the cheesecake rest inside for 1 hour.
06 - Remove the cheesecake from the oven and allow it to cool to room temperature. Transfer to the refrigerator and chill for at least 4 hours, preferably overnight, before serving.
07 - If using the topping, whisk together the sour cream, powdered sugar, and vanilla extract until smooth. Spread the mixture evenly over the chilled cheesecake just before serving.