Don't forget that your friend Stephen has this fascinating and entertaining book avail via Amazon (search for my name, Stephen Crout).
Okay, colcannon is apparently a Gaelic word meaning white-headed cabbage. Peter and I have made many variations of this over the years. Traditionally it is mashed potatoes with cabbage or kale. Our most recent version (last night) was made with collards and mashed potatoes. That's all the recipe you need. Make your favorite mashed potatoes, cook some greens, put them together. You are done.