Preheat oven to 350°F (175°C) and line a 9×13-inch baking dish with parchment paper, leaving an overhang for easy lifting.
In a medium bowl, mix graham cracker crumbs, 1/4 cup granulated sugar (crust), and 6 tablespoons melted butter until well combined. Press the mixture firmly into the bottom of the prepared baking dish to form the crust. Set aside.
In a large bowl, beat the softened cream cheese and 3/4 cup granulated sugar (cheesecake) until smooth and creamy. Add in the 2 eggs, one at a time, mixing well after each addition. Mix in the vanilla extract and 2 tablespoons of flour. Pour the cheesecake mixture over the crust and smooth the surface. Set aside.
For the blueberry layer, place the blueberries in a small bowl. Add 1 tablespoon lemon juice, 2 tablespoons cornstarch, and 1/4 teaspoon salt. Mix gently and spread the blueberry mixture evenly over the cheesecake layer.
For the crumble topping, in a medium bowl, combine 1 cup all-purpose flour, 3/4 cup granulated sugar (crumble topping), and cold cubed butter. Use a pastry cutter or your fingers to work until the mixture forms coarse crumbs. Sprinkle the crumble over the blueberry layer.
Place the baking dish in the oven and bake for 35 to 40 minutes, or until the crumble is golden brown and the center is mostly set. Allow to cool to room temperature and then refrigerate for at least 2 hours before slicing.
Remove from the pan using the parchment paper overhang. Slice into bars (about 12-16 pieces) and serve.