In a large bowl, combine all the ingredients except the flour. Mix with an electric mixer.
Slowly add in flour, continuing to mix on low speed.
Add the dough to the skillet and press down.
Place skillet in oven and check the cookie every 10 minutes or so. You want it to be not quite done when you pull it out, because it will continue baking a little bit. It takes me about 18 minutes.
Allow to cool slightly before drizzling with icing.
For the Icing:
Mix powdered sugar and milk until you get the consistency you like. Start with ½ cup powdered sugar and a few tablespoons of milk. Add more sugar and little milk until the icing is the thickness you want.
Drizzle icing on top of the cookie. Sprinkle more cinnamon on top.