
Place sweet potatoes in a large saucepan over high heat and cover generously with boiling water. Bring to a boil then reduce heat to medium, and cook uncovered until the sweet potatoes are fork tender, about 15-20 minutes.
Drain the sweet potatoes, and return to saucepan. Add the milk, butter, salt, pepper and cinnamon; mash with a potato masher to desired consistency.
Serve warm and garnish with thyme leaves.