Once the layers have cooled, add a layer of frosting to the top of your first layer and smooth out.
Build a wall of icing around the edge of the cake. Make sure this wall is tall and thick enough to hold in your chocolate ganache
Add a layer of chocolate ganache and top with the next cake layer.
Continue this process for the rest of the layers.
Frost the cake and top with chocolate ganache and toasted marshmallows. In a piping bag, add drips of chocolate down the cake. You can add other garnishes such as graham cracker crumbs around the base.