Preheat your oven to 325°F (163°C) and prepare an 8x8 or 9x13 inch baking pan by lining it with parchment paper. In a large bowl, combine the graham cracker crumbs, granulated sugar, and melted butter, mixing until well combined. The mixture should resemble wet sand. Press the crumb mixture firmly into the bottom of the prepared pan to form a crust, ensuring it’s evenly distributed. Bake the crust for about 10 minutes until it’s lightly golden. Once finished, remove it from the oven and allow it to cool completely.

While the crust cools, prepare the cheesecake filling for your Ravenclaw Blueberry Lemon Cheesecake Bars. In a large mixing bowl, beat softened cream cheese and granulated sugar together using an electric mixer until smooth and creamy, about 3-4 minutes. Add in the sour cream, vanilla extract, lemon zest, and lemon juice, and continue to mix until fully incorporated. Lastly, add the eggs one at a time, mixing gently after each addition until just blended. Be careful not to overmix, as this can cause cracks.

For the vibrant blueberry swirl, combine fresh or frozen blueberries, granulated sugar, and lemon juice in a medium saucepan. Cook the mixture over medium heat for about 5 minutes, stirring occasionally, until the blueberries start to soften and release their juices. In a separate small bowl, mix cornstarch with a splash of water to create a slurry, then stir this into the blueberry mixture. Cook for an additional 2-3 minutes until the sauce thickens slightly. Once thickened, you can strain it for a smoother sauce or blend it for a richer texture. Allow the blueberry sauce to cool.

Now it’s time to assemble your Ravenclaw Blueberry Lemon Cheesecake Bars. Pour the cheesecake batter over the cooled crust, spreading it evenly. Spoon dollops of the cooled blueberry sauce on top of the cheesecake layer, and using a toothpick or knife, gently swirl the sauce into the batter for that beautiful marbled effect. Bake in the preheated oven for 40-45 minutes. The center should be set but still slightly jiggly. Once done, turn off the oven and leave the bars to cool inside with the door propped open to prevent cracking.

After cooling, transfer the Ravenclaw Blueberry Lemon Cheesecake Bars to the refrigerator. Let them chill for at least 4 hours, or preferably overnight, to set completely. When you're ready to serve, sprinkle with edible silver or gold dust for an enchanting touch. Using a warm knife, slice the chilled dessert into bars for clean edges. Enjoy this magical treat, perfect for any Harry Potter-themed gathering!