Cast iron roast chicken with small potatoes

This is a recipe from the new Smitten Kitchen cookbook. Although I own the cookbook, I found the recipe online here: http://www.pink-parsley.com/2013/10/flat-roasted-chicken-with-tiny-potatoes.html?m=1. We removed the spine from this chicken and tried to cook it flattened, but our 12″ cast iron skillet was a bit small for a 3 ½ lb chicken. (Oct. 2015)