Wash and soak black chana and chana daal for about 5-6 hours in enough water.
Drain the water and rinse the soaked chana with fresh water.
Take the soaked kala chana andd chana daal in the pressure cooker and add water,salt ,black cardamom and ginger (water should be around 1.5 inch above the chana )
Now pressure cook for 6-7 whistles on medium heat.(or cook till chana/chickpeas become soft)
Grind tomatoes and green chilies and make a smooth paste.
Heat oil in a pan and add the cumin seeds and when they start to crackle add all the remaining tempering ingredients and saute till cumin become golden in colour.
Now add the tomato puree, turmeric, chili powder, black salt and coriander powder and cook till oil start separating from the sides of the masala.
Add the cooked chana, garam masala, mango powder,chopped boiled potato pieces in the tomato masala and cover the pan and simmer for 10 minutes.
Now add fresh coriander and serve hot with rice,pooris or parathas.