Place the potatoes in a large pot and cover with cool water by 2 inches. Bring to a simmer over high heat. Reduce the heat and simmer until tender when pierced with a fork, about 25 minutes. Drain in a colander, then spread evenly on a sheet pan.
Roast until the potatoes are dry but not browning, 15 to 18 minutes. Transfer to a bowl. Add the white chocolate to the hot potatoes and stir until the white chocolate starts to melt. Add the salt and nutmeg and stir to combine. Use a hand masher to mash the potatoes slightly. Pour in the milk and continue mixing until creamy, about 1 minute. Serve at once.
This recipe has been updated and may differ from what was originally published or broadcast.