Traditional Belgian potato purée: floury Bintje potatoes boiled tender, riced, and vigorously whipped with cold farmhouse butter, warm whole milk, an egg yolk, and freshly grated nutmeg.
Boil the potato quarters in salted water for 18 to 20 minutes until completely fork-tender.
Drain thoroughly and dry-steam over low heat for 1 minute. Pass immediately through a potato ricer into a warm bowl.
Beat the cold cubed butter into the hot potatoes with a wooden spoon. Stream in the warm milk, then beat in the egg yolk for rich golden colour and silky texture.
Season with plenty of freshly grated nutmeg and white pepper. Swirl into a warm bowl with a pat of butter on top and serve.