Steam or boil them for 30 minutes - steaming allows them to retain a bit of their starchiness, but boiling is easier.
Meanwhile, chop up the cabbage, ham and scallions.
Boil the cabbage over medium-high heat for 10 minutes until it turns slightly darker. Drain out the water and add 2 Tablespoons of the butter to the pot and return to heat. Saute for 5 minutes.
Reheat the ham however you prefer - you can add it to the pan with the cabbage, boil it, or heat it in the microwave.
When the potatoes are ready, drain and start mashing to remove all of the lumps, adding the butter in as needed to make mashing easier.
Heat the milk (either on the stove or in the microwave) and add it to the potatoes.
Season with salt and pepper and then stir in the cooked cabbage and ham, and sprinkle in the scallions.
Serve with generous Tablespoons of butter and a sprinkle of fresh chopped parsley.