Heat the oil in a large soup pot over medium heat. Add the onions, garlic, coriander, and chili flakes to the pot. Lower the heat until the sizzling sounds a bit lighter. Stir and sauté this mixture until the onions are stew-y and soft, but not browned, about 8-10 minutes. Add more oil if necessary.
Add the blood orange juice to the pot and stir. Add the sweet potatoes and stir again. Season everything with lots of salt and pepper. Add the stock to the pot and increase the heat. Once everything's boiling, bring it down to a simmer.
Cook the soup until the sweet potatoes are really tender, about 12-15 minutes. Purée the soup in batches in a blender or food processor until completely smooth. Adjust the seasoning if necessary. Serve the soup hot with little sweet potato chips and a sprinkle of sesame seeds if you like.
Juice from a regular orange or a splash or sherry vinegar would be just as nice as the blood orange.
Also, I garnish this with some little quickie sweet potato chips: just sauté some thin slices in olive oil over medium heat, remove when lightly browned, and then dust them with a bit of salt or spice of your choice (I used Old Bay seasoning).
Vegan sweet potato soup with coriander and blood orange is ready in less than 30 minutes with less than 10 ingredients. Topped with crisped up sweet potato slices for texture, this soup is so delicious and cozy!