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 bowl, combine the graham cracker crumbs, sugar, and melted butter until evenly moistened. Press the mixture firmly into the bottom of the prepared pan. Bake for 8 to 10 minutes until set. Let cool slightly.
03 - In a large bowl, beat the softened cream cheese and sugar until 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.
04 - Pour the cheesecake batter evenly over the cooled crust, spreading it into a smooth layer with a spatula.
05 - Toss the diced peaches with sugar, lemon juice, and cornstarch if using. Spread the peach mixture evenly over the cheesecake batter.
06 - 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.
07 - Refrigerate for at least 3 hours or until fully chilled and firm. Use the parchment overhang to lift the dessert from the pan, then cut into 12 bars.
08 - Whip the heavy cream with powdered sugar until soft peaks form. Drizzle or pipe over the chilled bars before serving.