Peel and cut the sweet potatoes into even chunks, about 1/2″. Add to pot and boil, covered, for about 12-15 minutes or until very tender when poked with a fork. Drain.
Mash potatoes. Add all but last two ingredients and stir until combined.
Add the raisins and marshmallows once the sweet potatoes aren’t too hot to melt the marshmallows. Serve.