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 granulated sugar together with 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 — do not overmix.
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 diced peaches with granulated sugar and lemon juice until coated. Distribute the peach pieces evenly over the cheesecake batter and gently press them in so they settle partially into the filling.
06 - Bake for 30 to 32 minutes, 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 throughout.
08 - In a chilled mixing bowl, beat heavy whipping cream with powdered sugar using an electric mixer until soft peaks form. Avoid overwhipping.
09 - Lift the chilled cheesecake from the pan using the parchment overhang. Slice into 12 even bars with a sharp knife, wiping the blade clean between cuts. Top each bar with a dollop of whipped cream if desired, and serve immediately.