I have this regularly for supper, and I tend to make life easier for myself by always having a stash of baked sweet potatoes in the fridge. If you don't, I advise baking the potatoes the night before, so that when you come to make this soup the next or another night, you are about 3 minutes away from a soothing, comforting, gutsily-flavoured big bowlful. But even if you do roast the sweet potatoes to order, as it were, you need do nothing while they're in the oven, and not much after.