Peel and dice your sweet potatoes into medium sized chunks. Place in large pot and boil.
Drain and mash potatoes with a potato masher or hand mixer in a large bowl.
In bowl of a stand mixer (or use electric mixer) combine mashed potatoes, brown sugar, melted butter, orange juice, and cinnamon.
Spread the sweet potato mixture evenly into prepared baking dish. Add the mini marshmallows to the top of the casserole.