Made this today, it's possibly the best soup I've ever made :)
Boil/simmer your leftover chicken carcass with 1 small onion and 2 teaspoons of vegetable boullion.
While this is boiling roast a reasonable size parsnip and a small butternut squash at 200'C for 1 hour.
Remove the carcass from the stock and carefully strip all the meat from the bones, returning it and bits of onion to the pot. Having peeled the squash chop it and the parsnip and add them to the pot.
Gather a handful of fresh basil and chop it up then add it to the pot.
Blend the soup.
I then sieved the soup as the parsnip had gone a bit woody.
Re-heat and eat with freshly baked bread.
Mmmmmmm.