Place the potatoes in a large pot and cover with cold water. Generously salt the water and bring to a boil. Reduce to a simmer and cook until fork-tender, about 20–25 minutes.
Drain the potatoes and let them cool slightly until manageable. Peel if not already done.
Pass the warm potatoes through a potato ricer or food mill into a large bowl until smooth.
Gradually fold in the cold, cubed butter, allowing it to melt into the potatoes while maintaining a creamy texture.
Slowly add the warm cream, folding gently with a spatula until the puree reaches a silky, smooth consistency.
Season with salt and white pepper to taste, adjusting for your preferred flavor.
For an ultra-smooth texture, press the mixture through a fine-mesh sieve using a spatula.
Transfer to a serving dish, dot with additional butter, sprinkle with flaky sea salt, and garnish with chopped chives. Serve immediately.
