Heat oven to 180C/160C fan/gas 4. Put all the veg on a large baking tray and toss together with rapeseed oil, garlic cloves in their skins, ground coriander, ground cumin and some seasoning. Roast for 45 mins, moving the veg around in the tray after 30 mins, until soft and starting to caramelise. Squeeze the garlic cloves out of their skins. Tip everything into a large pan. Add the chicken or vegetable stock, harissa paste and double cream. Bring to a simmer and bubble for a few mins. Blitz the soup in a blender, check the seasoning and add more liquid if you need to. Serve swirled with extra cream and harissa.