Peel and chop the sweet potatoes into even-sized cubes.
Place the sweet potato cubes in a large pot and cover with cold water.
Bring the pot to a boil over medium-high heat.
Cook the sweet potatoes for about 15-20 minutes or until tender.
Drain the sweet potatoes and return them to the pot.
Add the butter, milk, salt, and pepper to the sweet potatoes.
Mash the mixture using a potato masher or fork until smooth.
Stir in cinnamon if desired for added flavor.
Taste and adjust seasoning as needed.
Serve warm, garnished with a sprinkle of cinnamon or a pat of butter.