Grease an 8x8x2 baking pan. Beat butter for 30 seconds. Add 1/4 c sugar and salt, beating until fluffy. Stir in 1 c flour. Pat dough onto bottom of pan. Bake at 350 for 15 minutes. Meanwhile, beat eggs. Add remaining 3/4 c sugar, 2 Tbsp flour, lemon peel, lemon juice, and baking powder. Beat 3 minutes or until slightly thickened. Pour over baked layer. Bake at 350 for 25 to 30 minutes or until light golden brown around edges and center is set. Cool. Sift powdered sugar over top if desired. Cut into bars.