Chop your potatoes into small 1-inch chunks. You can peel them if you like, but it's not necessary. I find that leaving the peels on in this recipe gives it a rustic, hearty feel. Add the chopped potatoes to a large pot, then fill the pot with water and a teaspoon of sea salt. Bring the pot to a boil, then reduce the heat to low and allow the potatoes to simmer until they are tender enough to easily pierce with a fork. Pour the contents of the pan into a colander and allow the potatoes to drain.
While the potatoes are draining, add half of the butter to the same pot (no need to dirty another!) and heat it over medium until it's fully melted. Add the torn kale leaves with about 1/4 teaspoon of sea salt. Cook until the kale is completely wilted so it'll stir into the potatoes easily. It usually takes 3-5 minutes depending on the size of your pieces.
Add the green onions to the pot, stir to combine and cook for about a minute. Then add the potatoes back into the pot with half of the milk and the other half of the butter (or more if you like!).
It's time to mash the potatoes. I usually just do it with a fork because I mash them with the kale. You can get your hand mixer out if you really want them smooth, but I'd recommend doing that separately from the kale so you keep the texture. Continue adding more milk until you reach the consistency you like.
Transfer your Irish Colcannon to bowls and serve alone or topped with your favorite meat.