Soak the dried shiitake mushrooms in a bowl of water for 10 minutes to soften, remove the stems, and slice thinly.
Soak the dried wakame leaves in a little water for 5 minutes to reconstitute and slice the leaves into small pieces.
Place the sliced mushroom, wakame pieces, and the sliced daikon radish into a pot and add 3 cups of water.
Bring to a boil and cook, covered, for 5 minutes.
Purée the miso paste in a bowl with a little of the soup broth and then return the miso purée to the soup, stirring gently.
Simmer, uncovered, for a further 3 minutes.
Garnish each bowl of soup with chopped spring onion.