In a medium bowl, blend together the softened butter, 2 cups flour and 1/2 cup sugar. Press into the bottom of an ungreased 9x13 inch baking dish/pan.
Bake for 15 to 20 minutes, or until firm and golden. In another bowl, mix together the remaining 1 1/2 cups sugar and 2/3 cup flour. Whisk in the eggs and lemon juice. Pour over the baked crust.
Bake for an additional 20 minutes. The bars will firm up as they cool. For a festive tray, make another pan using limes instead of lemons and add a drop of green food coloring to give them a pale green color. After both pans have cooled, cut into 2 inch squares.