Separate dough into 16 triangles. Place one marshmallow on top of each dough triangle; sprinkle with chocolate. Wrap 1 dough triangle around each marshmallow, completely covering marshmallow and chocolate with dough; pinch edges of dough together to seal. Dip sealed sides in butter; place, sealed-sides down, in 16 muffin cups sprayed with cooking spray. Place muffin pans on baking sheet.