Beat butter, cream cheese, egg, and vanilla until light and fluffy.
Mix in dry cake mix. Cover and chill for 30-45 minutes until cool.
Preheat oven to 350. Lightly coat cookie sheet with cooking spray. Drop dough by tablespoons in a bowl of powdered sugar, roll into balls.
Bake for 12-14 minutes or until lightly golden brown. (If cookie tops are still yellow, check the bottom for done-ness.)