mmm that colcannon recipe looks yum.
i don't know the origins of it but my mom makes something similar. she uses spinach though.
basically you sautée a ton of spinach in a large pan (you have to use a lot because it turns to nothing when you sautée it) with some butter, garlic, salt, pepper and a dash of nutmeg. then you fold it into a big pot of home made mashed potatoes and add some cream for good measure. it's amazing.