Colcannon is a traditional and very uniquely Irish recipe perfect for St. Patrick's Day! Usually made with leftover mashed potatoes, milk, either thinly sliced kale or green cabbage, BUTTER, and scallions or chives. Of course, feel free to add your own spin with whatever you have - Swiss chard or arugula, pancetta or bacon, etc.
When I make mashed potatoes, I use Yukon gold potatoes (skin on), buttermilk, butter, salt, and pepper. I prefer the buttermilk because it adds a little depth of flavor to bland potatoes - and I am very generous with the salt and pepper. So, these are the leftover mashed potatoes that I'm starting with and I'll always have a bit of buttermilk left over in the fridge as well. If all you have is regular milk or even nut milk, just use whatever you have on hand.