Place the potatoes in a large pot and cover with cold water. Add a pinch of salt.
Bring to a boil over high heat. Reduce heat and simmer for 15-20 minutes, or until the potatoes are tender and easily pierced with a fork.
Drain the potatoes and return them to the pot.
While the potatoes are cooking, heat the milk in a small saucepan until warm.
In a separate pan, melt 2 tablespoons of butter over medium heat. Add the shredded cabbage and cook until tender, about 5-7 minutes.
Mash the potatoes with a potato masher or ricer until smooth.
Stir in the warm milk and remaining butter until well combined and creamy.
Fold in the cooked cabbage and chopped green onions. Season with salt and black pepper to taste.
Transfer the colcannon to a serving dish. Garnish with a little extra butter if desired.
Enjoy your meal!