Boil the potatoes in their skins until tender. Drain and leave until cool enough to handle.
Put the cabbage in a large pot and pour about 4 cups of boiling water over it. Cover and bring back to a boil and let steam about 10 minutes. Using tongs, pull the cabbage from the bottom to the top every few minutes for even cooking. Remove from heat and leave to sit.
Peel the potatoes and finely mash.
*NOTE: Spring onions are also known as scallions. You may also use one or two small onions, minced if you prefer.
Melt butter and add onion and cook until just tender. Add milk and heat through. Beat into potatoes. Season with salt and pepper.
Drain the cabbage thoroughly. Add potatoes and mix together.
Tip the mixture into a serving dish and sprinkle with a bit of nutmeg.