For the Crust
3/4 cup all-purpose flour, spooned into measuring cup and leveled-off
1/4 cup cornstarch
1/2 teaspoon salt
1/2 cup Confectioners’ sugar, plus more to decorate finished bars
1 stick (1/2 cup) cold unsalted butter, cut into 1/2-inch pieces
For the Lemon Topping
3 large eggs
1-1/2 cups granulated sugar
1 tablespoon lemon zest (be sure to zest before juicing the lemons)
5 tablespoons freshly squeezed lemon juice (from 2-3 lemons)
3 tablespoons all-purpose flour
Adjust an oven rack to the middle position and preheat the oven to 350°F.
Cover a 9-inch square baking pan with aluminum foil. 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.
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, about 10 seconds.
Sprinkle the mixture into the prepared pan and press firmly with your fingers into an even layer, building up a thin 1/2-inch edge around the sides (this keeps the filling from spilling beneath the crust).
Refrigerate for 30 minutes.
Bake the crust until lightly golden, 15-20 minutes.
In a medium bowl, whisk together the eggs, sugar, lemon juice, lemon zest, and flour.
When the crust is ready, give lemon mixture a quick final stir and then pour over top.