01 - Preheat oven to 350°F. Line a 9×9-inch baking pan with parchment paper, leaving an overhang on two sides for easy removal.
02 - In a medium bowl, combine graham cracker crumbs, granulated sugar, and melted butter, stirring until the mixture resembles wet sand. Press firmly and evenly into the bottom of the prepared pan. Bake for 8 minutes, then set aside to cool slightly.
03 - In a large bowl, beat softened cream cheese and sugar together using an electric mixer until completely smooth and free of lumps. Add eggs one at a time, beating well after each addition. Blend in vanilla extract and sour cream until just combined — avoid overmixing.
04 - Pour the cheesecake filling over the cooled crust, using a spatula to spread it into an even, smooth layer.
05 - In a separate bowl, toss the diced peaches with sugar and lemon juice until coated. Distribute the peaches evenly across the cheesecake surface, pressing them gently into the batter.
06 - Bake for 30 to 32 minutes, or until the edges are set and lightly golden while the center still has a slight jiggle. Remove from the oven and allow to cool completely at room temperature.
07 - Once cooled to room temperature, transfer the pan to the refrigerator and chill for at least 2 hours, or until the cheesecake is firm and well set.
08 - If using the topping, beat heavy whipping cream with powdered sugar in a chilled bowl until soft peaks form. Refrigerate until ready to serve.
09 - Using the parchment overhang, lift the cheesecake slab out of the pan and transfer to a cutting board. Slice into 12 even bars. Top each bar with a dollop of whipped cream before serving.