Yeah, Challenger is best for the recipe, as it gives a slight earthy / peppery character. However, I've made it with fuggles to bitter (just adjust the volume to match the alpha acid level), ind its pretty close. Glad you are giving the recipe a try. I drew my inspiration for it from the Garrison Martello stout, the St Ambroise Oatmeal Stout, and a porter that Dave made a few years ago... its tasty.