Spray a frying pan with low-calorie cooking spray and set on a medium heat. Add the onion and fry for 10 minutes.
Dissolve the stock cube into the water. Add the carrots, half the butter beans, coriander, and stock.
Bring to the boil, lower the heat, and cover. Simmer for 25-30 minutes, until the vegetables are soft.
Blitz with a stick blender until smooth. Add the remaining butter beans and return the pan to a low heat. Simmer for a few minutes until the beans are heated through. Season to taste with salt and pepper — and, if using, add the hot sauce.