Mix together pudding mix, powdered sugar, milk, and vanilla extract until combined.
Fold in thawed Cool Whip until smooth.
Let it set up in the fridge for 30 minutes to thicken slightly or frost your cake/cupcakes immediately.
Notes
Storage: Store Cool Whip frosting in an airtight container in the refrigerator for up to 4 days. Cakes and cupcakes frosted with it should also be refrigerated because the frosting contains milk and whipped topping.Use instant pudding: Make sure the box says instant pudding and pie filling, not cook-and-serve pudding.Keep refrigerated: Store the frosting and any frosted cakes or cupcakes in the refrigerator.