Preheat oven to 350F degrees.
Grease a 9x13-inch baking pan with cooking spray.
In a medium bowl, mix 2 cups flour, confectioner's sugar, and butter with your hands, or pastry blender, until well combined.
Press the mixture evenly into the bottom of the prepared pan.
Bake for 25 to 30 minutes or until the edges are golden.
Meanwhile, in a medium bowl, beat eggs, sugar, lemon zest, 4 tablespoons flour and lemon juice together with a whisk.
Pour lemon filling over the hot crust.
Bake for 15 to 20 minutes or until the center is set.
Cool the lemon squares/bars on a wire rack.
When cool, cut into desired size and shape, and dust with additional powdered sugar if desired.
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