This is my secret to decorating sugar cookies. The technique is called flooding and I've found that these bottles are perfect for decorating--it reminds me of coloring in a coloring book. You can find these bottle in the candy making section at Michaels or Wal-Mart.
In order to get a nice smooth finish I microwave the bottles for 5-10 seconds and repeat as necessary. Depending on the type of decorating that I am doing I adjust the amount of powdered sugar or corn syrup I use. If you want to stack the cookies (which can be done without damaging the frosting) use less corn syrup--but know that you will have to microwave the bottles more frequently while decorating.
This is the recipe that I've devised--its a cross between a frosting and an icing.
canterbury bee icing
2 lbs powdered sugar
1 package (8 oz) cream cheese
¾ cup of light corn syrup
1-2 teaspoons pure almond or vanilla extract
pinch of salt
directions--mix cream cheese in mixer until smooth. Add half the powdered sugar and corn syrup and mix until smooth. Continue to alternate adding powdered sugar and corn syrup until desired consistancy is reached. Add almond extract and salt to taste. (the recipe above will yield an easy-to-work-with icing, but may not stack as well as a mixture with less corn syrup)