01 - Preheat oven to 350°F. Line a 9x9-inch baking pan with parchment paper, leaving an overhang on two sides for easy bar removal.
02 - In a medium bowl, combine graham cracker crumbs, granulated sugar, and melted butter, stirring until the mixture resembles wet sand. Press the crumb mixture 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 the softened cream cheese and granulated sugar on medium speed until completely smooth and free of lumps. Add the eggs one at a time, mixing well after each addition. Blend in the vanilla extract and sour cream until fully incorporated. Pour the batter evenly over the cooled crust.
04 - Toss the 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.
05 - Bake for 30 to 35 minutes, or until the center is just set with a slight jiggle. Remove from the oven and allow the bars to cool completely at room temperature.
06 - Refrigerate the cooled bars for at least 3 hours, or until thoroughly chilled and firm. Use the parchment overhang to lift the slab from the pan, then cut into 12 even squares.
07 - In a chilled bowl, whip the heavy cream with powdered sugar using an electric mixer until soft peaks form. Drizzle or pipe the whipped cream over the sliced bars just before serving.