In a large glass bowl, beat egg yolks. Add the milk and continue beating. When smooth and bubbly on top, add 1 cup of the sugar and 3 tablespoons of the cornstarch. Beat until well combined.
Cover the bowl with plastic wrap and puncture a hole in top with a knife. Cook in microwave on HIGH for three minutes. Whisk and re-cover with plastic wrap. Microwave on HIGH for another two minutes. Add vanilla and butter. Mix well and add banana slices.
In another bowl, beat egg whites and add the remaining tablespoon cornstarch and the three tablespoons of sugar. Beat well until stiff peaks form. Spread the meringue over the pudding mixture. Bake at 400 degrees F. for 6 to 8 minutes or until brown. When done, line pudding with vanilla wafers.