Set a frying pan with 4 tbsp oil over a low heat. Add half the gram flour and stir well. Tip in the remaining flour and toast for 5-6 minutes, stirring. When the flour changes colour slightly and has a nutty aroma, remove from the heat and leave to cool.
Tip the flour into a large bowl and gradually whisk in 500ml water. Stir in 500ml more water, then pass through a sieve.
Cook the green beans in a pan of boiling salted water for 4-5 minutes. Drain, then refresh in cold water. In the same pan, boil the potatoes for 15 minutes, then drain.
Set a heavy-based pan with the remaining oil over a medium heat. Fry the cumin seeds for 1 minute, then fry the fenugreek seeds for 5 seconds. Stir in the asafoetida, curry leaves and green chillies. Cook for 10 seconds, then add the ginger, turmeric and chilli powder. Fry for 20 seconds.
Pour in the gram flour mix and cook, stirring, for 3-4 minutes. Add 400ml water and bring to the boil, then reduce the heat to low and simmer for 2 minutes.
Add the jaggery and tamarind, then season with salt. Add the drumsticks, cover and cook for 16-18 minutes, stirring regularly.
Stir in the okra. Cook for 20 minutes, topping up with more water if needed, until tender. Add the beans and potatoes and warm through for 5 minutes.