Dice the onions and throw them into the oil in a pot on low to medium heat. Let the onion cook slowly for about five minutes - it should begin to turn clear.
Peel and the chop the sweet potatoes into cubes.
Dice the bell pepper, garlic and ginger and add to the pot. If you’re using dried herbs, add them now. Add the cinnamon and cayenne pepper too. Cook for another two minutes and then add the peanut butter, soy sauce, vinegar and tomato.
Add a splash of broth and stir well.
Chuck in the sweet potatoes and rest of the broth, and simmer on a medium heat. If you’re using fresh herbs, add them now. Stir occasionally and after 10-15 minutes check the sweet potatoes are soft (poke one with a knife and it should slide in).
Season with salt and pepper, maple syrup and lime juice and give another stir. If you used a cinnamon stick then fish it out now.
Using a hand liquidiser or (blender if you don’t have one), give the soup a blend. That’s it - done!
Garnish with peanuts and serve with a side if wanted - fresh bread is an obvious choice!