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, 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 - Using an electric mixer, beat softened cream cheese and sugar in a large bowl on medium speed 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 incorporated — avoid overmixing.
04 - Pour the cheesecake filling over the cooled crust, spreading into an even layer with a spatula.
05 - In a separate bowl, toss diced peaches with sugar and lemon juice until coated. Distribute peach pieces evenly across the cheesecake surface, gently pressing them partially into the batter.
06 - Bake for 30 to 32 minutes, or until edges are lightly golden and the center is set but still has a slight jiggle. The filling will continue to firm as it chills.
07 - Allow the cheesecake to cool completely at room temperature, then transfer to the refrigerator and chill for at least 2 hours until firm and well set.
08 - If using the topping, beat cold heavy cream with powdered sugar in a chilled bowl until soft peaks form.
09 - Lift the chilled cheesecake from the pan using the parchment overhang. Slice into 12 even bars and top each with a dollop of whipped cream before serving.