Place potatoes into a large pot and cover with salted water; bring to a boil. Reduce heat to medium-low and simmer until tender, about 20 minutes.
Meanwhile heat milk and cream in a saucepan until warmed.
Drain potatoes and press through a potato ricer or mash. Season with nutmeg and white pepper. Pour in warm milk and cream. Add grated cheese, creme fraiche, butter, and garlic; mix until well combined and creamy. Season with salt to taste.
