Peel the potatoes, cut into pieces, place in a saucepan of boiling water and simmer for 20 minutes. Drain well, return to the pan over a low heat and, shaking the pan, allow the excess moisture to steam off. Mash the potatoes until smooth – for perfect mash try using a hand-held ricer.
Place the butter and milk in a saucepan over a medium heat and gently bring to the boil. Slowly pour the melted butter and hot milk into the potatoes, mixing well with a rubber spatula. Break in the egg and beat. Finally, add the nutmeg and seasoning. Mix well, taste and adjust to your personal choice. Serve at once.