Preheat oven to 300. In a large bowl, cream together butter and confectioners sugar; then blend in flour and salt. Press mixture down in a flat buttered cookie pan. Bake at 300 for 20 minutes.
While crust is baking, in a medium bowl blend together eggs, granulated sugar, lemon juice and rind. Pour over crust. Raise temperature to 350 and bake for an additional 15-20 minutes at 350.
Remove from oven and let cool. When cooled, sprinkle with additional confectioners sugar. Cut into rectangles.