Preheat oven to 375 degrees F (190 degrees C). Grease a 9x13 inch baking dish.
Bring a pot of water to a boil. Add sweet potatoes and cook until tender, about 15 minutes. Drain and mash with butter, sugar, milk, salt and lemon zest. Shape mixture into balls, with a marshmallow in the center of each. Roll in cereal crumbs and place in prepared dish.
Bake in preheated oven for 20 minutes, or until marshmallows begin to ooze.