Heat your oven to 200°C/Fan 180°C/Gas 6. Set a large roasting tin on the top shelf to heat up.
Scrub your carrots and chop into 3-4cm pieces. Tumble into the warmed tin. Gloss with 1 tbsp oil. Season well. Roast for 20 mins till tender and golden at the edges.
Peel and finely chop your onion. Trim the top and bottom off the leek. Rinse out any grit and finely slice it. Add the onion and leek to the carrots after they have roasted for 20 mins. Cook for 10 mins or till everything is tender.
Scoop the veg into a blender with 500 ml warm water and your stock cube (or 500 ml hot homemade stock). Peel and chop the orange. Add it to the blender. Blitz till smooth. Whizz in more water or stock if you think it needs it. Season to taste.
Ladle into warm bowls. Top with coriander leaves and a drizzle of tamarind to serve.