In a medium saucepan, combine fresh blueberries, granulated sugar, and lemon juice over medium heat. Gently mash the berries with a fork until they begin to break down, then mix cornstarch with a little water and stir it into the blueberry mixture. Cook for about 5-7 minutes until thickened, then strain to remove skins, and let it cool.

Set your oven to preheat at 325°F (160°C), preparing it for baking the Mini Lemon Blueberry Cheesecakes.

In a mixing bowl, blend together graham cracker crumbs, granulated sugar, and melted butter until fully combined. Press this mixture firmly into the bottom of lined muffin cups to create a solid crust. Bake in the preheated oven for about 5 minutes until lightly golden, then remove and let them cool completely.

In a large bowl, beat the cream cheese and granulated sugar with an electric mixer until smooth and creamy. Gradually add in fresh lemon juice, lemon zest, and vanilla extract, blending well. Incorporate the eggs one at a time at low speed to keep the filling smooth and avoid overmixing.

Carefully fill the cooled crusts with the cheesecake filling, leaving a little space at the top. Drizzle the cooled blueberry sauce over the filling and use a toothpick to gently swirl it in for a beautiful marbled effect.

Place the assembled cheesecakes in the oven and bake for 17-20 minutes. The Mini Lemon Blueberry Cheesecakes are ready when the edges are set but the centers still have a slight jiggle.

After baking, allow the cheesecakes to cool in the pan for about 1 hour at room temperature. Once cooled, transfer them to the refrigerator and chill for at least 3-4 hours or overnight to ensure they are fully set.