Luxurious Viennese potato purée: floury Austrian mountain potatoes riced fine, whipped with plenty of warm milk, cold Alpine butter, and grated nutmeg until cloud-soft and creamy.
Place the potato chunks in a large pot, cover with cold water, and add the cooking salt. Bring to a boil and cook for 18 to 20 minutes until completely fork-tender.
Drain all water thoroughly. Return the pot to low heat for 1 minute, shaking gently so the potatoes dry out completely. Pass the hot potatoes immediately through a potato ricer into a clean bowl.
Using a wooden spoon or spatula, beat the cold cubed butter into the hot riced potatoes until fully absorbed. Gradually stream in the hot milk, beating rhythmically until a silky, light, airy purée forms.
Season with freshly grated nutmeg, white pepper, and sea salt. Swirl into a warmed serving bowl and garnish with a tiny melting pat of butter on top.