In a large pot, combine the boiled water, soy sauce, miso, rice vinegar and sesame oil. Whisk everything together until the miso is fully dissolved. Add the mushrooms, tofu, carrot, garlic and ginger.
The recipe is designed to be made in conjunction with a low-cost store-cupboard. Bring 1.5 litres/2½ pints water to the boil in a large saucepan. Once boiling, stir in the stock cubes and miso paste.