We first tried this Irish dish on St. Patrick's Day one year, and it quickly became a standard in our family. It is basically mashed potatoes with cooked cabbage, so feel free to play with the recipe - a lot! I don't measure anything in this recipe, so I will attempt to relate amounts here.
Potatoes, cut in chunks, to steam or boil in a 3-4 qt. pot, filled. I place celery leaves and bay leaves on top of the potatoes for flavor and then throw the leaves away when done cooking. Cook until tender.
One green cabbage, diced about 1/2", to steam or boil in another 3-4 qt. pot. Cook until tender.
I drain my potatoes, add one stick butter, and mash by hand. Add drained cabbage, s/p to taste, and then add plain (I like Bulgarian) yogurt to taste. I use about 3 cups. Serve!
This works well to then put in a crockpot and take to a potluck if you put the colcannon in while hot. If you try to start a crockpot with cold colcannon, it will take a few hours because it is so dense (not recommended!).