1Preheat oven to 350 degrees F (175 degrees C). Spray 12 muffin cups with cooking spray.
2Combine sugar and cinnamon in a bowl. Separate biscuits. Place a marshmallow in the center of each biscuit and wrap biscuit dough around marshmallow. Press dough to seal marshmallow completely. Roll dough ball in melted butter, then roll in cinnamon-sugar mixture. Arrange each dough ball in the prepared muffin cups.
3Bake in the preheated oven until golden brown, about 15 minutes.