Grease muffin cups or line with paper baking cups.

In a mixing bowl, combine biscuit mix, sugar, milk, egg and melted butter; stir well (batter will be slightly lumpy).

Spoon batter into muffin cups. Dip marshmallows into remaining butter, then into cinnamon-sugar mixture.

Push a marshmallow into each muffin, making sure that marshmallow is completely covered by batter (or the marshmallow will leak out when baking).

Bake at 400ºF for 15 to 20 minutes.