Mix together sugar and cornstarch and slowly add milk. This should be cooked in the top of a double boiler, but you can cook it over low to medium heat, stirring constantly until it thickens--do not leave it unattended.

Slightly beat egg yolks and temper with a small amount of the hot custard; stir well. Add egg mixture to custard pot and cook 2 more minutes.

Remove from heat and add vanilla and butter. Let cool. In a 9 by 9-inch oven proof baking dish, alternate pudding, bananas, and wafers, beginning with pudding and ending with pudding.

Beat egg whites and cream of tartar until soft peaks form. Gradually add sugar until stiff peaks form, then spread onto top of pudding mixture. Bake until golden brown.