Place borlotti beans in bowl, cover with water, cover, stand overnight; drain.
Add broad beans to pan of boiling water, simmer, uncovered, 5 mins; drain, rinse under cold water, Peel skins from broad beans; discard skins.
Heat butter in pan, add onion, leek and celery, cook, covered, stirring occasionally, about 10 mins or until vegetables are soft. Add flour, cook, stirring, until mixture is dry and grainy. Remove from heat, gradually stir in stock, pepper, sugar and saffron. Stir over heat until mixture boils and thickens, add borlotti beans, simmer, covered, about 50 mins or until beans are tender. Add broad beans, kumara and cabbage, simmer, uncovered, about 10 mins or until kumara is tender; stir in coriander.