Heat the butter until the foam subsides. Add the diced chopped onions, sprinkle with salt, stir to coat with butter. Add the chopped carrots along with the spices. Stir and cook until softened, about 10 minutes. Add the stock; there should be enough to cover the vegetables. Bring the pot to a boil over high heat. Reduce the heat to medium and continue cooking until the carrots are cooked through, about 10 to 15 minutes. If you have an immersion blender, purée the soup in the pot. If not, wait until the soup cools slightly, and purée in a food processor. Add enough coconut milk (and a little more stock or water if necessary) to bring the soup to the consistency you want. Adjust the seasoning (depending on the stock you use, you may need more or less salt), and lime juice to taste. Garnish and serve.