Put the sweet potatoes in a pot with 8 cups of cold water and 1 tablespoon of coarse salt. Bring to a simmer, cover, and cook until a knife slips in the sweet potatoes easily and cleanly, about 30 minutes. Drain the sweet potatoes and peel the skin off.

Mash the sweet potatoes using the back of a big spoon. You may also use a potato masher. If you want a silky smooth texture, transfer the mashed sweet potatoes to a food processor or electric mixer to process until it becomes a very fine and creamy texture.

In a small sauce pan heat up the milk and bring to a boil. Meanwhile, transfer the mashed sweet potatoes to a Dutch oven. On medium-low heat, add the chilled butter cubes to the sweet potatoes and stir continuously for a smooth and creamy texture, about 5 minutes. 

Pour in the hot milk, stirring briskly. Keep stirring until all the milk is absorbed. Turn off the heat and add salt and ground white pepper.

Serve the mashed sweet potatoes immediately. Sprinkle some Maldon sea salt flakes, chopped parsley and two small cubes of butter on top of the mashed sweet potatoes before serving.