Preheat your oven to 350°F (175°C). Line a 9x13-inch baking pan with parchment paper. In a large mixing bowl, combine flour, sugar, and salt. Cut in cold butter until resembling coarse crumbs. Press into the prepared pan, then bake for 20-25 minutes until golden.

In a medium bowl, whisk together eggs and sugar until combined. Add in flour, lemon juice, lemon zest, vanilla extract, and salt. Mix until smooth, then gently fold in blueberries.

Pour the blueberry filling over the crust evenly. Smooth with a spatula. Return to oven at 325°F (160°C) and bake for 30-35 minutes until filling is set and lightly jiggles.

Allow to cool completely in the pan on a wire rack for about 2-3 hours. Cut into squares or bars and dust with powdered sugar before serving.