I have tried making this soup with homemade pumpkin puree. It was perfectly edible...but not quite so nice in my opinion. I think the pumpkin benefits in flavour and texture by being cooked in the stock, alongside the other ingredients. But if you want to avoid preparing a whole pumpkin, give it a go. (If you are looking for an easy way to make pumpkin puree at home, put the entire pumpkin in the slow cooker, and cook for a few hours until soft. That way it's so easy to scoop the flesh out with no cutting required!)