01 - Preheat the oven to 350°F. Line a 9x9-inch baking pan with parchment paper, leaving an overhang on two sides for easy removal.
02 - In a medium bowl, combine the graham cracker crumbs, granulated sugar, and melted butter 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 - In a large bowl, beat the softened cream cheese and granulated sugar with an electric mixer until completely smooth. 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 if using. Spread the peach mixture in an even layer over the cheesecake batter.
05 - Bake for 30 to 35 minutes, or until the center is set with only a slight jiggle. Remove from the oven and allow to cool to room temperature.
06 - Refrigerate the bars for at least 3 hours, or until completely chilled and firm. Use the parchment overhang to lift the slab from the pan, then cut into 12 even bars.
07 - In a chilled bowl, whip the heavy cream with powdered sugar until soft peaks form. Drizzle or pipe over the sliced bars before serving.