Preheat your oven to 350°F. Peel the sweet potatoes and cut into cubes.
Boil the sweet potatoes in a large saucepan until very soft, about 20 minutes. Drain the cooked sweet potatoes and transfer them to a bowl.
Add 1 tablespoon of butter, salt, pepper, nutmeg, cinnamon.
Mash the sweet potatoes with a fork until smooth and add splashes of the milk as you go.