Preheat your oven to 325°F (160°C). Prepare a 9x9 inch baking pan by greasing it lightly and lining it with parchment paper.
In a medium-sized mixing bowl, combine the graham cracker crumbs, melted butter, and ¼ cup sugar. Press this mixture into the bottom of the prepared pan. Bake for 10 minutes and allow to cool slightly.
In a large mixing bowl, beat the softened cream cheese on medium speed until smooth. Gradually add in the remaining ½ cup of sugar, mixing on low speed until fully incorporated.
Add the eggs to the cream cheese mixture one at a time, mixing well after each addition. Then mix in the fresh lemon juice, lemon zest, and vanilla extract until smooth.
In a small bowl, toss the fresh blueberries with the 2 tablespoons of cornstarch. Gently fold the blueberries into the cream cheese mixture.
Pour the cream cheese mixture over the pre-baked crust, spreading it evenly. Bake for 30-35 minutes, or until the edges are firm and the center has a slight jiggle.
Allow the cheesecake bars to cool in the pan for about 30 minutes at room temperature. Then transfer to the refrigerator and chill for at least 2 hours.
Once chilled, use the parchment paper overhang to lift the bars out of the pan. Cut into squares and serve chilled.