Start by placing fresh blueberries, sugar, and lemon juice into a medium saucepan over medium heat. Stir gently while bringing the mixture to a simmer for about 5-7 minutes, mashing the berries as they cook. Once bubbling, mix cornstarch with a tablespoon of water, then add it to the pan. Cook for an additional 2-3 minutes until thickened, then strain the sauce through a sieve to remove skins and seeds, and allow it to cool completely.

Preheat your oven to 325°F (163°C) while you prepare the crust. In a mixing bowl, combine graham cracker crumbs with sugar and melted butter, stirring until evenly moistened. Line your muffin pan with cupcake liners, then pack the crumb mixture into each cup. Bake for 5-7 minutes until set and golden, then let them cool to room temperature.

In a large mixing bowl, beat the cream cheese and granulated sugar together using an electric mixer on medium speed until smooth and creamy, around 2-3 minutes. Gradually blend in the lemon juice, lemon zest, and vanilla extract. Lower the mixer speed and add the eggs one at a time, mixing just until combined.

Once your crusts have cooled, evenly distribute the cheesecake filling over each crust using a spoon or piping bag. Take the cooled blueberry sauce and swirl it gently into the cheesecake filling.

Carefully place your muffin pan into the preheated oven and bake for 17-20 minutes. They should appear set at the edges but slightly jiggly in the center. Let them cool at room temperature for about 1 hour.

Transfer the pan to the refrigerator and allow them to chill for at least 3-4 hours, or until fully firmed up.