Pre-heat oven to 350°F. Line an 8x8-inch baking pan with aluminum foil, allowing a 1-inch overhang on each side. Spray the foil with cooking spray.
To make the crust, add flour, corn starch, powdered sugar and butter to the bowl of a food processor. Pulse until the mixture resembles damp sand.
Pour into the prepared pan and spread into an even layer. Using the palms of your hands or the bottom of a glass, pack the crust down to form an even and tight base. Bake for 20 minutes.
While the crust is baking, make the filling by whisking together the eggs and sugar in a medium bowl until smooth. Add the flour and mix until no clumps remain.
Add the lemon juice, zest and salt. Stir to combine. When the crust is ready, reduce the oven temperature to 325°F. Pour the filling immediately into the hot crust and bake for 25 to 30 minutes, until the center is set.
Allow to cool completely in pan on a cooling rack. Use the foil to remove cooled slab onto a cutting board. Cut into 16 even bars and dust with powdered sugar.