01 - Preheat the oven to 325°F. Line a 9x9-inch baking pan with parchment paper, allowing extra overhang on the sides for easy bar removal.
02 - Combine graham cracker crumbs, granulated sugar, and melted butter in a medium mixing bowl. Mix until the crumbs are evenly moistened. Press the mixture firmly into the bottom of the prepared pan to form an even crust.
03 - In a large mixing bowl, beat softened cream cheese and sugar with an electric mixer until completely smooth. Add eggs one at a time, incorporating each before the next addition. Blend in vanilla extract and sour cream until no streaks remain.
04 - Spread the cheesecake batter evenly over the crust using a spatula. Bake for 40 to 45 minutes, until the edges are lightly golden and the center is nearly set. Remove from oven and set aside to cool to room temperature.
05 - Transfer the pan to the refrigerator and chill for at least 3 hours to set completely.
06 - Once fully chilled, top the cheesecake evenly with chopped strawberries and blueberries in a decorative patriotic pattern. Drizzle melted white chocolate over the berries, if desired.
07 - Lift the bars from the pan using the parchment overhang. Cut into 16 even squares and serve chilled.