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 - Combine graham cracker crumbs, granulated sugar, and melted butter in a medium bowl until the mixture resembles wet sand. Press firmly and evenly into the bottom of the prepared pan. Bake for 8 to 10 minutes until lightly golden. Set aside to cool slightly.
03 - Using an electric mixer, beat softened cream cheese and sugar on medium speed until completely smooth and free of lumps. Add eggs one at a time, mixing well after each addition. Blend in vanilla extract and sour cream until fully incorporated.
04 - Pour the cheesecake batter evenly over the cooled crust, using a spatula to spread it into a smooth, level layer.
05 - Toss diced peaches with granulated sugar, lemon juice, and cornstarch in a bowl until evenly coated. Spread the peach mixture in a single layer over the cheesecake batter.
06 - Bake for 30 to 35 minutes until the center is just set with a slight jiggle. Remove from the oven and allow to cool completely at room temperature.
07 - Refrigerate the pan for at least 3 hours, or until the cheesecake layer is fully chilled and firm. Use the parchment overhang to lift the slab out of the pan, then cut into 12 even bars.
08 - Whip heavy cream with powdered sugar until soft peaks form. Drizzle or pipe over the chilled bars just before serving.