01 - Preheat oven to 325°F (163°C). Line a 9x9-inch baking pan with parchment paper, allowing excess to hang over the sides for easy removal.
02 - In a medium mixing bowl, combine graham cracker crumbs, granulated sugar, and melted butter. Press the mixture firmly into the base of the prepared pan to form an even layer.
03 - In a large bowl, beat softened cream cheese and granulated sugar with an electric mixer until smooth and creamy. Incorporate eggs one at a time, mixing thoroughly after each addition. Blend in pure vanilla extract and sour cream until fully uniform.
04 - Pour cheesecake filling over the crust, smoothing the top evenly. Bake for 40 to 45 minutes or until the center is just set and the edges have a light golden color. Cool completely at room temperature.
05 - Transfer the pan to the refrigerator and chill for at least 3 hours to allow the bars to set completely.
06 - Once thoroughly chilled, top evenly with chopped strawberries and blueberries to create a patriotic pattern. Drizzle with melted white chocolate if desired. Use the overhanging parchment to lift out and cut into 16 bars. Serve bars cold.