In a large mixing bowl beat egg whites and a dash of salt with an electric mixer until soft peaks form. Gradually add 1/4 cup of the sugar, beating until stiff peaks form.
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 extract. Fold egg yolk 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 top of pan.) Bake in a 350 degree F oven for 8 to 10 minutes or until lightly browned.
Transfer cookies on parchment or in molds to a wire rack. Cool cookies for 15 minutes. Remove ladyfingers from parchment or molds, then completely cool on the wire rack.
Just before serving, spread about 2 teaspoons apricot preserves on flat side of half of the ladyfingers. Top with remaining ladyfingers, forming sandwiches. If desired, store unfilled ladyfingers in the freezer until the day of serving.
