Deseed the squash and cut into wedges.
Heat the oven to 180°C and roast for about 30 mins until golden and soft. Transfer to a plate, let it cool, then scrape the squash meat off the skin. Discard the skin. ( N.B. this step can be done in advance but then keep the squash meat chilled until you continue with the recipe)
Finely chop the onion and garlic. Deseed the chilli, then chop finely.
Heat the oil in a saucepan and add the onion, garlic and most of the chilli. Cover and cook on a very low heat for 15 minutes or so, until the onions are soft.
Add the squash meat and the stock then, using a handheld blender, whizz until smooth.
Serve with swirls of crème fraîche or Greek youghurt (if liked) and scatter the remaining chopped chill on top.