Firstly roughly chop the squash (disposing of the seeds) and onion into large chunks, and crush the garlic.
Put a small amount of oil into a roasting tin and throw in the squash, onions, garlic and thyme.
Roast in a pre-heated oven for 30-40 minutes at 180 C / Gas 4, or until all the ingredients have a nice caramelised colour on them, but not burnt.
Warm up the stock, and then put all of the roasted vegetables into a blender, with a couple of spoonfuls of the stock and blend.
Depending on how thin or thick you like your soup, you can now add more stock, if you find that you have put too much stock in, it isn't a problem, just place the soup into a saucepan and slowly boil until the soup has reduced to the consistency that you want.
Now all you need to do is season with salt and pepper, serve and grate parmesan into the soup. Enjoy with a nice wedge of crusty bread. Add chilli sauce to taste.
