In a mixing bowl, combine graham cracker crumbs, granulated sugar, and melted butter until you achieve a sandy texture. Press this mixture firmly into the bottom of a lined 9x9-inch baking dish to create a solid crust.

Using an electric mixer, beat the cream cheese in a large bowl until it's smooth and creamy, about 2 minutes. Gradually add sugar and sour cream, mixing until fully combined and silky. Carefully fold in the fresh or frozen blueberries gently coated with cornstarch.

Pour the luscious cheesecake filling over the prepared graham cracker crust, using a spatula to smooth the top evenly. Ensure to distribute the blueberries throughout the filling by swirling slightly.

In a separate bowl, mix flour, granulated sugar, and cold diced butter to create the crumb topping. Blend until it resembles coarse crumbs. Sprinkle this mixture evenly over the cheesecake filling.

Preheat your oven to 350°F (175°C). Bake the Blueberry Cheesecake Bars for 45-55 minutes. Look for the center to be set but still slightly wobbly, and the top should be lightly golden.

Once baked, allow the dish to cool at room temperature for about an hour. Then, refrigerate the bars for at least 4 hours, preferably overnight, to allow flavors to meld and filling to set properly.