This frosting is best made and served just before serving. Anything that you don't eat should be put in the fridge ASAP as the consistency of Cool Whip will change as it warms to room temperature.
Also if you make extra just freeze it!
1c Cool Whip
3 oz of cream cheese
1 1/4 cup powdered sugar
1t Vanilla extract
1/4c butter softened
In a mixing bowl combine all ingredients and beat with a hand mixer until smooth. It may be a bit runny if your Cool Whip has thawed. Use a spatula to spread t. If you want to thick frosting add in more powdered sugar and less Cool Whip.