Preheat oven to 350°F (175°C). Line a 9x13 inch baking pan with parchment paper, leaving an overhang for easy removal.

Prepare the Crumble/Crust: In a large bowl, whisk together flour, 0.75 cup sugar, baking powder (if using), and salt. Cut in the cold butter using a pastry blender or your fingers until the mixture resembles coarse crumbs. Add the 1 egg and mix until just combined. Press about 2/3 of this mixture evenly into the bottom of the prepared pan for the base.

Prepare the Blueberry Filling: In a separate bowl, gently toss the blueberries with 0.25 cup sugar, cornstarch, and lemon zest until coated. Set aside.

Prepare the Cheesecake Layer: In a medium bowl, beat the softened cream cheese until smooth. Gradually beat in 0.5 cup sugar and vanilla extract until creamy. Beat in the remaining 1 egg until just combined, taking care not to overmix.

Assemble the Bars: Spread the cheesecake mixture evenly over the crust base. Carefully spoon dollops of the blueberry filling over the cheesecake layer. Sprinkle the remaining 1/3 of the crumb mixture evenly over the top of the blueberries.

Bake for 50 to 55 minutes, or until the topping is golden brown and the edges of the cheesecake are set (the center may still have a slight wiggle). Let cool completely on a wire rack before chilling in the refrigerator for at least 4 hours before cutting into bars.