Best Ever Lemon Bars with Buttery Shortbread Crust

Ingredients

• 1¾ cups all-purpose flour, (spooned into measuring cup and leveled-off)
• ¼ cup cornstarch
• 1 teaspoon salt
• 1 cup confectioners' sugar, (plus more to decorate finished bars)
• 1 cup (2 sticks) cold unsalted butter, cut into ½-in (13-mm) pieces
• 6 large eggs
• 3 cups granulated sugar
• 2 tablespoons lemon zest ((be sure to zest the lemons before juicing))
• 2/3 cup freshly squeezed lemon juice, (from 5 to 6 lemons)
• ⅔ cup all-purpose flour, (spooned into measuring cup and leveled-off)