In a large bowl, combine flour, cornstarch, powdered sugar, salt, and cold cubed butter.
Using two forks, mash butter into the dry ingredients until it is fully incorporated.
Line a 9x13 inch (22 x 33 cm) baking dish with parchment paper and coat with a non-stick spray. Pour the mixture into the pan and pack it down firmly, allowing for some to come about ½ inch (1 ¼ cm) up the sides of the pan.
Refrigerate the crust for 30 minutes, then bake for 20-25 minutes or until it develops a light golden brown color.
Allow the crust to cool while you prepare the filling & reduce the oven temperature to 325˚F (160˚C).
In another large bowl, combine the eggs, sugar, and flour. In a blender, blend strawberries, lemon zest, lemon juice, and milk until well combined.
Pour the blended mixture into the egg mixture and stir well. Pour the filling over the partially baked crust and immediately put the pan into the oven.
Bake at 325˚F (160˚C) for 45 minutes, or until it doesn't jiggle when you shake the pan (times and temperatures may vary). Allow to cool for 30-45 minutes and remove from pan. Cut into 24 even squares & sprinkle with powdered sugar.