Cook the potatoes in salted water until tender. Drain and return to the heat briefly to dry out.
While the potatoes are cooking, warm the milk in a pan with the spring onions. Simmer on a low heat until the onions are soft. Turn the heat out and leave to infuse.
Once the potatoes have dried out mash them well before adding the milk and onion mixture and as much butter as you wish. Beat well together and add the nutmeg. Season to taste with the salt and white pepper.