Our White Icing recipe uses 1 cup powdered sugar- plus 1 tablespoon milk, adding milk 1 teaspoon at a time. To thin it out- simply add the full 3 teaspoons milk.
If you are using the Betty Crocker Cookie Icing in a pouch- it is not meant to thin out. The icing dries to a shiny hard consistency so cookies can be stacked.
Thanks for your question.
Answered 12/18/2012 by jturnbull