In a medium bowl, combine 2 cups flour, the butter, and 1 cup confectioners sugar; mix until crumbly. Press into bottom of a 9- x 13-inch baking dish to form a crust; bake 15 minutes.
Meanwhile, in a large bowl, with an electric beater on medium speed, beat remaining 1/2 cup flour, the granulated sugar, eggs,lemon juice, and lemon extract until well blended. Pour over hot crust.
Bake 25 to 30 minutes, or until set.
Allow to cool then cut into squares. Dust with extra confectioners sugar and serve.