Position the oven rack in the center and preheat the oven to 350°F. Line a 9x13-inch metal baking pan with heavy-duty aluminum foil, ensuring the foil extends beyond the edges to create handles for easy lifting later. Press the foil into the corners and up the sides of the pan, overlapping as needed for full coverage. Lightly coat the foil with nonstick cooking spray.

Combine the flour, cornstarch, confectioners' sugar, and salt in a food processor. Pulse a few times to mix. Add the cold butter cubes and pulse until the mixture resembles a coarse, crumbly texture, about 10–15 seconds. Transfer the crumbly dough into the prepared pan and press firmly with your fingers to form an even layer. Build up the edges slightly, about ¾ inch high, to prevent the filling from seeping under the crust. Chill the crust in the refrigerator for 30 minutes or freeze for 15 minutes to set.

Bake the crust for 15 to 20 minutes, or until it turns lightly golden. Set aside while preparing the lemon filling.

In a large mixing bowl, whisk together the eggs, granulated sugar, lemon juice, lemon zest, and flour. Mix thoroughly to ensure no lumps remain, creating a smooth batter.

Once the crust is ready, give the lemon filling one final stir to recombine any settled ingredients. Pour the filling over the warm crust, ensuring an even layer, and immediately return the pan to the oven. Bake for an additional 30 to 35 minutes, or until the filling is set and firm to the touch.

Allow the lemon bars to cool completely on a wire rack, which may take several hours. To cut, lift the bars from the pan using the foil overhang and transfer them to a cutting board. Gently peel the foil from the edges, using a knife to assist if needed. Slice into squares or triangles as desired. Dust generously with confectioners’ sugar through a fine sieve before serving.

Store the bars in an airtight container in the refrigerator for up to 4 days. They can be enjoyed chilled or at room temperature.