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 mixing 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 lightly golden. Set aside to cool slightly.
03 - In a large bowl, beat the softened cream cheese and sugar with an electric mixer 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, using a spatula to spread it into an even layer.
05 - In a separate bowl, 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 and only slightly jiggly when gently shaken. Remove from the oven and allow to cool to room temperature.
07 - Refrigerate for at least 3 hours or until fully chilled and firm. Lift the bars out of the pan using the parchment overhang and cut into 12 even squares.
08 - In a chilled bowl, whip the heavy cream with powdered sugar until soft peaks form. Drizzle or pipe over the sliced bars before serving.