Cook potatoes in salted water for 5 to 10 minutes until tender.
Drain most of the water and continue cooking on low heat until fully softened.
Drain fully, peel the potatoes, and mash with most of the butter while hot.
Boil milk, peas, and spring onions in a saucepan for 5 minutes.
Stir in the parsley and remove the saucepan from the heat.
Gradually combine potatoes with the milk mixture, adjusting for desired consistency.
Season with salt and pepper and beat until the mixture is creamy.
Serve hot with the remaining butter melting in the center.