Put a very large saucepan on a medium heat and pour in a couple of glugs of olive oil.
Add the sage leaves and fry for around 30 seconds or until dark green and crisp. Quickly remove them with a slotted spoon to a bowl lined with paper towels - you'll use these for sprinkling over at the end. In the pan you'll be left with a beautifully flavored oil, so put it back on the heat and throw in your onion, celery, carrot, garlic, rosemary leaves, chile and a good pinch of salt and pepper. Cook gently for about 10 minutes until the vegetables are sweet and soft. Add the squash and the stock to the pan, bring to the boil and simmer for around 30 minutes.
While the soup is cooking, make your croutons. Drizzle a little olive oil over the ciabatta slices, and press some grated Parmesan onto each side. Place in a non-stick pan without any oil and fry until golden on both sides.
When the squash is soft and cooked through, whiz the soup with an immersion blender or pour it into a standard blender and pulse until you have a smooth puree* (but you can leave it slightly chunky if you like). Most importantly, remember to taste and season it until it's perfect. Divide the soup between your bowls, placing 2 croutons on top of each. Sprinkle with a few of your crispy sage leaves and drizzle with a swirl of good-quality extra-virgin olive oil.
*When blending hot liquids: Remove liquid from the heat and allow to cool for at least 5 minutes. Transfer liquid to a blender or food processor and fill it no more than halfway. If using a blender, release one corner of the lid. This prevents the vacuum effect that creates heat explosions. Place a towel over the top of the machine, pulse a few times then process on high speed until smooth.
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