Make the shortbread cookie dough. Chill for one hour. Roll out the dough and cut out the cookies. Place on a baking sheet lined with parchment paper and bake for 10 minutes until golden.
Make the chocolate ganache and set aside to let cool and thicken to a buttercream consistency.
Pipe or dollop the ganache on one shortbread cookie, place the toasted marshmallow on top of the ganache, and sandwich with another shortbread cookie. Enjoy!