Preheat your oven to 350°F (175°C).
Peel and cube the sweet potatoes. Boil them until tender, about 15-20 minutes.
Drain the sweet potatoes and mash them in a large mixing bowl.
Add brown sugar, melted butter, milk, eggs, vanilla extract, cinnamon, and salt to the mashed sweet potatoes, then blend until smooth.
Pour the sweet potato mixture into a greased baking dish, spreading it evenly.
If desired, sprinkle mini marshmallows evenly across the top.
Bake in the preheated oven for 25-30 minutes until heated through and marshmallows are golden brown.
Remove from the oven and allow to cool slightly before serving.