Mix sugar, salt, and cornstarch or flour. Gradually add to milk. Stir over low heat until thick. Stir a small amount of hot mixture into eggs. Then pour back into remaining hot mixture while beating. Continue cooking about 2 minutes, or until thickened. Remove from heat. Add butter or margarine and vanilla. Chill thoroughly. Hot fillings change the flavor of the bananas. Line pie shell with half of filling. Slice bananas over filling (save a few slices for top). Cover with remaining filling. Top with whipped cream and banana slices. Serve immediately.