8 oz. softened cream cheese (I used 1/3 less fat)
1/2 stick softened butter
1 egg yolk
1 tsp. vanilla
1 yellow butter cake mix
Mix first 5 ingredients together and refrigerate for 2 hours. Form into balls (will be very sticky - put extra powdered sugar on your hands to roll easier) and roll completely in powdered sugar. Bake on ungreased cookie sheet for 8-10 minutes at 350º.
They will look/seem undercooked, but pull them out and put on cooling rack.
They will be PERFECT!
These are really good served cold.
From ModHousewife: http://www.modhousewife.com/2011/12/gooey-butter-cookies/