Steam the potatoes in their skins for 30 minutes.
Once they're soft, peel the potatoes using a knife and fork. Then, chop them with a knife.
Mash the potatoes thoroughly to remove any lumps.
Add half of the stick of butter in small pieces to the mashed potatoes.
Gradually pour in the hot milk while stirring continuously. Season with a few grinds of salt and black pepper to taste.
Boil the shredded cabbage in water without adding salt until it becomes a darker color.
Add 1 tablespoon of butter to the boiled cabbage to make it tender, and cover it with a lid for 2 minutes.
Drain the cabbage thoroughly and then return it to the pan, chopping it into small pieces.
In a large saucepan, put the cooked ham and cover it with water.
Bring the water to a boil and let it simmer for 45 minutes or until the ham is tender.
Drain the ham and remove any excess fat, then chop it into small pieces.
Combine the chopped cabbage, finely chopped scallions, and chopped ham with the mashed potatoes. Gently stir everything together.
To serve, portion the colcannon into individual soup plates.
Make an indentation on the top of each serving by swirling a wooden spoon.
Place 1 tablespoon of butter into each indentation, and finish by sprinkling with chopped parsley.