1.Cover beans with cold water in a medium bowl; stand overnight. Drain beans, rinse under cold water; drain. Place beans in a medium saucepan of water; bring to the boil, drain. Add fresh water to the pan; bring to the boil. Simmer, partially covered, for about 1 hour or until beans are tender; drain.
2.Meanwhile, heat oil in a medium pan over medium-high heat; add mustard seeds, cumin seeds, curry leaves, turmeric, ground coriander, cumin, green chillies, garlic and ginger. Cook, stirring, for about 1 minute or until seeds begin to pop. Add sugar, salt, tomatoes and the stock. Bring mixture to the boil, then simmer, uncovered, for 5 minutes.
3.Add kidney beans and broad beans; simmer, partially covered, for about 5 minutes or until beans are heated through and tender. Season to taste with salt and pepper.
4.Serve with yoghurt and mint, if desired.
For a shortcut, use a rinsed and drained 400g can of red kidney beans and begin at step 2.Note