In heavy saucepan, dissolve corn starch in water; stir in sweetened
condensed milk and egg yolks. Cook and stir until thickened and
bubbly. Remove from heat; add butter and vanilla. Cool slightly.
Slice 2 bananas; dip in lemon juice and drain. Arrange on bottom of
prepared crust. Pour filling over bananas; cover. Chill 4 hours or
until set. Spread top with whipped cream. Slice remaining banana; dip
in lemon juice, drain, and garnish top of pie. Refrigerate leftovers.