Peel and cut your potatoes into small pieces and place in a pot. Add water to just cover the potatoes. Add a pinch of salt, and then bring the potatoes to the boil. Once boiling, lower the heat to medium and then simmer for approximately 10 minutes until the potatoes are fork tender.
Meanwhile bring another pot of water (filled about ¾ full) to the boil. Add your chopped cabbage along with a pinch of salt, and boil for about 2 minutes. Lower your heat to medium and simmer for another 8 minutes or so.
Once your potatoes and cabbage are tender drain. Add the potatoes back to the pot, along with 5 tablespoons of butter, and your milk. Mash the potatoes until creamy and smooth. Then add your drained cabbage, and salt and pepper to taste.
Last but not least, add your sliced green onions and stir. Place the potatoes in a bowl, and make a shallow well in the middle. Add the remaining tablespoon of butter to the well, and add a generous amount of pepper.
Enjoy this colcannon with corned beef, any meat, or on its own!