In a small saucepan over medium heat, combine fresh blueberries, sugar, and lemon juice. Gently mash the blueberries with a fork for about 5 minutes. Once bubbling, mix a tablespoon of cornstarch with water, add it to the mixture, and cook until thickened (about 2-3 minutes). Strain the sauce to remove skins and set aside to cool completely.

Preheat your oven to 325°F (160°C).

In a mixing bowl, combine graham cracker crumbs, granulated sugar, and melted butter until moistened. Evenly distribute the mixture into a muffin pan lined with cupcake liners and press down firmly. Bake for about 5 minutes until the crust feels set, then allow to cool completely.

In a large bowl, beat together room temperature cream cheese and granulated sugar until smooth. Gradually blend in fresh lemon juice, lemon zest, and vanilla extract. Beat in eggs one at a time until just combined without overmixing.

Spoon the cheesecake mixture into the cooled crusts, filling each about three-quarters full. Add a dollop of the cooled blueberry sauce on top and swirl with a toothpick or knife.

Bake for 17-20 minutes until the edges are set with a slight jiggle in the center.

Let the mini cheesecakes cool at room temperature for about 1 hour. Cover with plastic wrap and refrigerate for 3-4 hours or overnight.