Line a cookie sheet with parchment or plain brown paper. Set aside. In a large mixing bowl beat egg whites and dash of salt with an electric mixer until soft peaks form (tips curl). Gradually add 1/4 cup of the sugar, beating until stiff peaks form (tips stand straight). In a small bowl beat egg yolks on medium speed for 1 minute. Gradually add remaining sugar, beating until thick and lemon colored. Beat in lemon peel, lemon juice, and vanilla. Fold egg yolks mixture into egg whites. Fold in cake flour. Spoon batter into a decorating bag fitted with a large round tip ( about 1/2 inch in diameter). Pipe 3 1/2 x 3/4 inch strips of batter 1 inch apart on the prepared cookie sheet. (or, spoon batter into ungreased ladyfinger molds until batter is even with the top of the pan). Sift powdered sugar over cookies. Bake in a 350F oven for 8 to 10 minutes or until lightly browned. Transfer cookies on paper or in the ladyfinger molds to a wire rack. Cool cookies for 15 minutes. Remove ladyfingers from the paper or molds, then completely cool on the wire rack. If desired, store unfilled ladyfingers in the freezer until the day of serving. Just before serving, spread about 2 teaspoons of the Lemon Curd Filling on the flat side of half of the ladyfingers. Top with remaining ladyfingers, forming sandwiches. Lemon Curd Filling: In a sauce pan combine 1/3 cup of sugar and 2 teaspoons cornstarch Stir in 2 teaspoons finely shredded lemon peel, 1/4 cup lemon juice, and 1/4 cup butter (or margarine). Cook and stir until thickened and bubbly. Stir half of the mixture into 2 beaten eggs. Return mixture to pan. Cook and stir for 2 minutes. Cover with waxed paper; cool. Makes about 1 cup.