Dissolve the cornstarch in the milk. Add the egg and yolks and incorporate. In a saucepan combine the milk and sugar and bring to a boil. Temper into the yolk mixture. Return to a boil and whisk for 1 minute. Stir in vanilla and butter. Cool. When chilled whisk to lighten and fold in whipped cream. Cut bananas and toss in lemon juice. Stir in bananas.
