In a medium saucepan, combine fresh blueberries, sugar, and lemon juice over medium heat. Mash the blueberries slightly as they cook for about 5 minutes until they start to release their juices. In a separate bowl, mix cornstarch with a little water, then add it to the pan, stirring continuously for 2-3 minutes until the mixture thickens. Strain to remove skins and seeds, then set aside to cool.

Preheat your oven to 325°F (160°C). In a mixing bowl, combine graham cracker crumbs, sugar, and melted butter until well-blended. Line a muffin pan with cupcake liners, and evenly press the crust mixture into the bottom of each liner to form a solid base. Bake in the preheated oven for about 5 minutes until lightly golden, then allow to cool completely while you prepare the filling.

In a large mixing bowl, beat softened cream cheese and granulated sugar together until smooth and creamy, about 2-3 minutes. Gradually add in lemon juice, zest, and vanilla extract, mixing until well combined. Incorporate room temperature eggs, one at a time, mixing gently to maintain fluffiness and avoid overmixing.

Using a spoon or piping bag, fill each cooled crust with the cheesecake mixture, leaving a little space at the top. Drizzle the prepared blueberry sauce over the filling and use a toothpick or skewer to gently swirl it, creating a marbled effect.

Place the assembled cheesecakes in the oven and bake for 17-20 minutes. The edges should be set, but the centers should have a slight jiggle. Be careful not to overbake, as this can lead to cracks forming.

Once baked, remove the mini cheesecakes from the oven and let them cool at room temperature for about 1 hour. After they’ve cooled, refrigerate the cheesecakes for at least 3-4 hours, or preferably overnight.