Bring the stock to the boil in a large saucepan. Add the carrots and lentils, bring the mixture back to the boil, then cover and simmer over low heat for about 8 minutes, or until the carrot and lentils are soft.
Meanwhile, heat the oil in a pan, add the onion and cashews and cook over medium heat for 2-3 minutes, or until the onion is soft and browned. Add the curry paste and cilantro and cook for a further minute, or until fragrant. Scrape the mixture into the carrot and lentil mixture.
Blend the soup until very smooth. Then return to medium heat to warm it up before serving. Season to taste with salt and and pepper. Serve garnished with coriander and a dollop of yogurt.