Add the milk, egg yolks, ⅔ c sugar, corn starch and salt into a large microwave-safe glass bowl. Use a whisk to blend vigorously for 30 seconds.
Cook in the microwave on HIGH for 5-7 minutes, whisking well after each minute.
After 4 minutes, whisk every 30 seconds.
Once it begins to thicken, make sure to whisk it vigorously to smooth it out.
Once it's thick like a pudding should be, it's done cooking.
Stir in the vanilla and butter, until the butter is completely melted.
Press plastic wrap over the surface to prevent a skin from forming. Let cool in the fridge (or in an ice bath if you're in a hurry!).
Once the pudding is cool, spread it over the cream cheese and banana layer.
Arrange the vanilla wafers (or graham crackers) over the pudding and return to the refrigerator.