I register this photo on behalf of J. Marsh, her comment:
Here is the fungus with standard sized roo poo for scale.
The white inner bit feels exactly like fresh marshmallow.
It was about 4 or 5 meters away from the corner of the fence near where we were weeding Patterson’s curse.
This is the spongy, spore-free base and all that remains once the powdery spores have been dispersed by wind. Earlier stages of this type of fungus can be seen at http://canberranaturemap.org/Community/Sightings/Details/2458956 and http://canberranaturemap.org/Community/Sightings/Details/2459154.