01 - Preheat 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 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. Remove and let cool slightly.
03 - In a large bowl, beat softened cream cheese and sugar together until completely smooth. Add eggs one at a time, mixing well after each addition. Blend in vanilla extract and sour cream until fully incorporated. Pour the batter evenly over the cooled crust.
04 - Toss diced peaches with sugar, lemon juice, and cornstarch if using. Spread the peach mixture evenly over the cheesecake batter layer.
05 - Bake for 30 to 35 minutes until the center is set with only a slight jiggle. 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 slab out of the pan, then cut into 12 even bars.
07 - Whip heavy cream with powdered sugar until soft peaks form. Drizzle or pipe over the chilled bars before serving.