Line a 13x9 inch baking pan with parchment paper, leaving an overhang for easy lifting.
In a medium bowl, stir together graham cracker crumbs, 1/2 cup granulated sugar, and melted butter until the crumbs are evenly moistened.
Press the crumb mixture firmly and evenly into the bottom of the prepared pan, using the bottom of a measuring cup to compact it well.
Bake the crust at 350°F for 10 to 12 minutes until lightly golden, then let it cool completely and chill in the refrigerator while you prepare the filling.
In a small saucepan, combine blueberries, 1/4 cup granulated sugar, and lemon juice over medium heat and cook, stirring often, until the berries start to break down and release their juices, about 5 to 7 minutes.
In a small bowl, whisk cornstarch and water until smooth, then stir the mixture into the blueberries and cook for 1 to 2 minutes more until thickened; remove from heat and let the blueberry mixture cool to room temperature.
In a large mixing bowl, beat softened cream cheese, 3/4 cup granulated sugar, and vanilla bean paste with an electric mixer until very smooth and creamy, scraping down the sides of the bowl as needed.
In a separate bowl, beat cold heavy cream and powdered sugar with an electric mixer on medium high speed until stiff peaks form.
Gently fold the whipped cream into the cream cheese mixture with a spatula until fully combined and smooth, keeping the mixture light and airy.
Pour about 3/4 of the cooled blueberry mixture into the cream cheese filling and gently swirl it through with a spatula, or fold in fully if you prefer a uniform blueberry color.
Pour the cheesecake filling over the chilled crust, spreading it into an even layer with a spatula and tapping the pan lightly on the counter to release air bubbles.
Spoon the remaining blueberry mixture over the top in small dollops and use a toothpick or knife to swirl it into a marbled pattern.
Cover the pan tightly and refrigerate for at least 4 hours, preferably overnight, until the cheesecake layer is firm.
Remove the chilled slab from the pan using the parchment overhang; use a sharp knife dipped in hot water and wiped dry between cuts to slice into 24 bars.
Serve the bars chilled, garnished with fresh blueberries and mint leaves if desired, and store leftovers in an airtight container in the refrigerator for up to 5 days.