Combine flour, sugar, salt and eggs in a medium saucepan. Beat with hand beater or wire whip until well mixed. Add milk gradually and continue beating until smooth. Cook over medium heat until mixture thickens, stirring constantly. Remove from heat. Stir butter and 1 ts. vanilla into hot mixture. Place in refrigerator.
Slice bananas into cooked pie shell. Remove custard from refrigerator and spoon over bananas. Whip whipping cream until soft peaks form. Gradually add sugar and whip until stiff. Fold in remaining vanilla. Spread over pie, sealing edges. Refrigerate and serve very cold.