To serve four, use four large sweet potatoes.  Peel your sweet potatoes and cut them into two-inch chunks.  Put them in a thick saucepan with a cup of whole milk to which you've mixed in a tablespoon or two of brown sugar, and heat the milk slowly until it is just simmering.  Put a lid on the pan and cook the sweet potatoes until tender (about 20 minutes).  Add four pats of butter, salt, pepper, and spices (allspice, cinnamon, whatever your prefer) to taste, and mash the mixture together.  Serve immediately.  You retain all the nutrition of the sweet potatoes, but they are amazingly moist and have a delicious texture.   We eat these year round, not just at Thanksgiving.