Peel the sweet potatoes and cut them into evenly sized chunks.
Place the sweet potato chunks in a large pot and cover with water.
Bring the water to a boil over medium-high heat.
Cook the sweet potatoes for about 20 minutes or until tender.
Drain the sweet potatoes and return them to the pot.
Add the butter to the sweet potatoes and let it melt.
Pour in the milk and mash the sweet potatoes until smooth.
Season with salt, pepper, and cinnamon, if using.
Mix well until all ingredients are combined.
Taste and adjust seasoning as needed before serving.