Place the broad beans in a bowl and cover with cold water, soak overnight to hydrate them. The following morning, drain the beans and pop the skins off of them.
Heat the olive oil in a large saucepan and add the onion, leek, potato and dried beans and cook, stirring for 6 minutes. Stir in the paprika, cumin and cook for 5 minutes, add the celery, garlic and stock and simmer gently, covered for about 1 hour or until the beans are soft and breaking up, adding some extra stock if you need it. Do not add any salt whilst the beans are cooking as this will cause them to toughen.
Remove from the stove, add the butter and blend the soup until it is smooth for a creamy finish. Add the fresh fava beans and season with salt and pepper. If the soup is too thick then thin it down with a little more liquid. To serve, ladle the soup into bowls and sprinkle with the garnish ingredients and some chopped herbs.