Heat your oven to 200°C/Fan 180°C/Gas 6. Scrub the carrots and chop into 1cm-thick batons. Scatter into a roasting tin. Sprinkle over 1 tsp ground coriander and a good pinch of salt and pepper. Drizzle over 1 tbsp oil and toss well till evenly coated. Slide into the oven to roast for 20 mins, till golden on the outside and tender in the middle.
Meanwhile, peel and crush the garlic. Separate the coriander leaves and stalks and finely chop the stalks (save the leaves for later).
Bring a dry pan to a medium-high heat. Add the cashews. Fry for 2-3 mins, turning frequently, till toasted on all sides. Tip into a bowl. Reduce the heat of pan to medium and add 1 tbsp olive oil.
Slide the garlic and coriander stalks into the pan along with a pinch of salt and pepper. Fry for 1 min, stirring frequently. Top up with 750ml boiling water and crumble in the stock cube. Bring to the boil, then reduce to a simmer and keep warm.
When the carrots are cooked, transfer to the pan and use a stick blender to whizz everything into a smooth soup. No stick blender? Pour the soup (in batches if needed) into a blender and blitz. Squeeze in half of the lemon juice and have a taste. Add more salt and pepper if needed.
Roughly crush the cashews. Finely chop the coriander leaves. Ladle the soup into deep bowls and sprinkle over the nuts and coriander. Serve with wedges of the leftover lemon half.