Wash and soak ½ kg white kidney beans for 5 hours.
Add the soaked beans to a pressure cooker with 1.5 litres water, 1 black cardamom, and 1 tsp salt. Pressure cook for 30 minutes, or until the beans are soft.
In another pan, heat ½ cup oil. Add chopped onions and sauté until golden brown.
Add cumin seeds and ginger garlic paste. Cook for a few seconds until fragrant.
Add blended tomatoes and cook well.
Add salt, red chilli powder, crushed red chillies, turmeric powder, and coriander powder. Mix well and cook until the oil starts to separate.
Add yogurt and tamarind pulp. Cook for 2 minutes on medium flame.
Add the boiled lobiya and cook for another 5 minutes.
Lightly mash some of the beans with a spoon to make the gravy thick and creamy.
Add 1½ cups water, cover, and cook on low flame for 15 minutes, or until you reach your desired consistency.
Add green chillies, fresh coriander leaves, and garam masala.
Serve hot with roti, naan, or boiled rice.