01 - Preheat the oven to 350°F. Line a 9x9-inch baking pan with parchment paper, leaving an overhang on the sides for easy removal.
02 - In a medium bowl, combine the graham cracker crumbs, granulated sugar, and melted butter. Stir 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. Remove and let cool slightly.
03 - In a large bowl, beat the softened cream cheese and granulated sugar with an electric mixer until completely smooth and creamy. 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 - In a separate bowl, 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 remaining. Remove from the oven and allow to cool completely to room temperature.
06 - Refrigerate the cheesecake bars for at least 3 hours or until fully chilled and firm. Use the parchment overhang to lift the block from the pan. Cut into 12 even bars using a sharp knife.
07 - In a chilled bowl, whip the heavy cream with powdered sugar until soft peaks form. Drizzle or pipe over the bars just before serving.