Preheat oven to 350 F. Place sweet potatoes into a large saucepan over medium heat, cover with water and bring to a boil. Let simmer until potatoes are fork tender. Drain and place into a large bowl.
Mash potatoes with butter, salt, and cinnamon. Unroll crescent rolls and separate into triangles. Press each into a greased muffin cup. Spoon the sweet potato filling into each cup. Bake for 15-20 minutes.
Top each with one marshmallow. Bake for another 3-4 minutes.