Wisk cornstarch, sugar, and salt in a medium saucepan. Add the egg yolks, milk, and butter on low heat until thick. Remove from heat and add the vanilla.
Meanwhile, beat egg whites with mixer until fluffy. Add the egg whites to the cooked mixture. Line the bowl (I use a trifle bowl) with vanilla wafers and bananas. Pour 1/2 of the mixture over the vanilla wafers.
Put vanilla wafers and banana slices over that layer. Pour pudding over the wafers and bananas. Put wafers over the last layer. Refrigerate and ready to serve.