Step 1

Adjust an oven rack to the middle position and preheat the oven to 350°F.

Step 2

Cover a 9x13-in metal baking pan with heavy-duty aluminum foil (see note below). Push the foil neatly into the corners and up the sides of the pan, using two pieces if necessary to ensure that the foil overlaps all edges (the overhang will help removal from the pan). Spray the foiled pan with nonstick cooking spray.

Step 3

Place the flour, corn starch, salt and Confectioners' sugar in the bowl of a food processor fitted with the blade attachment and mix for a few seconds. Add the butter and mix to blend until the mixture resembles coarse meal, 10 to 15 seconds. Sprinkle the mixture into the prepared pan and press firmly with your fingers into an even layer, building up a thin ¾-inch edge around the sides (this keeps the filling from spilling beneath the crust). Refrigerate for 30 minutes or freeze for 15 minutes.

Step 4

Bake the crust until lightly golden, 15 to 20 minutes.

Step 5

In a large bowl, whisk together the eggs, sugar, lemon juice, lemon zest, and flour. Be sure no lumps of flour remain.

Step 6

When the crust is ready, give lemon mixture a quick final stir and then pour over top. Immediately return the pan to the oven and bake another 30 to 35 minutes, or until the topping is set and firm. Let the bars cool on a rack to room temperature; it will take several hours.

Step 7

To cut, use the foil overhang to lift the baked square out of pan and onto a cutting board. Carefully loosen the foil from the edges of the crust, using a knife if necessary. Using a sharp knife, cut into squares or triangles. Use a fine sieve to dust the squares with Confectioners' sugar. Store the bars in a covered container in the refrigerator for up to 4 days. Serve chilled or room temperature.

Step 8

Freezer-Friendly Instructions: The bars can be frozen for up to 3 months. After they are completely cooled, freeze the batch whole, covered tightly with aluminum foil or plastic freezer wrap. Before serving, remove them from the freezer and let them thaw overnight in the refrigerator. Cut the bars and then sprinkle with Confectioners’ sugar before serving.

Step 9

Note: Be sure to use heavy-duty aluminum foil; regular aluminum foil may stick. Parchment paper can also be used to line the pan.