For the icing, I used about 4 cups powdered sugar and a 1/4 cup of milk. You can add more/less powdered sugar depending on how thick you want the icing to be.
Other optional ingredients:
-Mini M&Ms (Christmas colors)
-2 rolls of Life Savers (mixed colors)
Step 1: AT-AT Body
Step 2: AT-AT head
I attached the head piece to the body with a roll of Life Savers.