To prepare the oven,set the temperature to 350 degrees F(175 degrees C) and allow it to preheat.
Put the sweet potatoes into a big saucepan and addsufficient water to cover them. Bring the water to a boil and allow the sweetpotatoes to cook until they become tender, typically around 15 minutes. Takethe saucepan off the heat, strain out the water, and then proceed to mash thesweet potatoes.
In a sizable bowl, put in the mashed sweet potatoes. Combinewith brown sugar, margarine, orange juice, and cinnamon using an electric mixeruntil thoroughly blended. Evenly distribute the mixture into a 9x13 inch bakingdish, and then add a layer of marshmallows on top.
Cook the casserole in the oven that has been preheated untilit is warmed throughout and the marshmallows turn puffy and acquire a goldenbrown color, which usually takes 25 to 30 minutes.