Bake cupcakes according to boxed instructions and allow to cool completely
Frost your cupcake with your frosting
Take your marshmallows and cut them in half diagonally (You'll need about 20 "petals" per cupcake)
Place the marshmallows into a Ziploc bag
Add your sanding sugar to the Ziploc bag and shake
Apply your marshmallow petals to your frosted cupcake - starting outside and working toward the center
Enjoy!