Preheat the oven to 350°F (180°C). Line a 9x13 inch (22 x 33 cm) baking dish with parchment paper and coat with a non-stick spray.
In a large bowl, combine 1 ¾ cups of flour, the cornstarch, powdered sugar, salt, and butter. Using two forks, mash butter into the dry ingredients until it is fully incorporated.
Pour the mixture into the prepared pan and pack it down firmly against the bottom and about ½ inch (1 ¼ cm) up the sides. Refrigerate the crust for 30 minutes,
Bake the crust for 20-25 minutes, or until it develops a light golden brown color. Remove from the oven and let cool while you prepare the filling. Reduce the oven temperature to 325°F (160°C).
In a separate large bowl, whisk together the eggs, granulated sugar, and remaining 3 tablespoons of flour.
In a blender, combine strawberries, lemon zest, lemon juice, and milk and blend until well-combined.
Pour the strawberry mixture into the egg mixture and whisk well. Pour the filling over the partially baked crust and immediately put the pan into the oven.
Bake for 45 minutes, or until the filling doesn't jiggle when you shake the pan (times and temperatures may vary). Remove from the oven and let cool for 30-45 minutes.
Use the parchment to lift the bars from the pan. Cut into 24 squares and dust with powdered sugar.
