Mix the cornstarch, sugar, and salt in a saucepan over low heat. Slowly add the milk and cook until the mixture begins to thicken, about 10 minutes, stirring constantly. Put the eggs in a small bowl and slowly whisk in a ladleful of the hot milk to temper the eggs. Add the milk-egg mixture back to saucepan and cook for 2 more minutes, stirring constantly. When thick, remove from heat and stir in the vanilla and butter. Mix well to combine and set aside to cool to room temperature. Refrigerate covered with plastic wrap, until well chilled.
In a large bowl or individual bowls, add a layer of vanilla wafers, a layer of bananas and a layer of pudding. Repeat with remaining ingredients. Top with whipped cream and serve.