Rinse 1 cup dried red kidney beans in a colander, then soak them in plenty of water overnight for 8 to 12 hours.

Drain the soaked red kidney beans and rinse them well under cold running water.

Dice 2 medium onions, 2 tomatoes, and the 1-inch piece of fresh ginger. Slit 2 green chilies lengthwise.

Heat 2 tbsp vegetable oil in a large heavy pot over medium heat. Add half of the diced onion, 1/2 tsp cumin seeds, 1/2 tsp coriander seeds, 1 sprig curry leaves, ginger, salt, and green chilies.

Fry the aromatics for 6 to 8 minutes until the onion is deep golden brown. Stir often to prevent the spices from burning.

Add the diced tomatoes and 1 heaped tsp tomato paste. Cook for 4 to 5 minutes until the tomatoes soften and turn jammy.

Stir in 1 tsp Kashmiri chili powder, 1 tsp paprika powder, a pinch of turmeric powder, 1/4 tsp garam masala, 1/2 tsp ground coriander, and 1/2 tsp ground cumin. Cook the masala for 5 to 8 minutes over low heat.

Add the drained kidney beans and 2 cups water to the masala. Bring the curry to a boil while stirring.

Cover the pot and simmer the curry for 45 to 60 minutes until the kidney beans are completely tender. Add more hot water as needed to maintain a thick gravy.

Thinly slice the remaining onion and strip the leaves from the remaining curry leaf sprig. Measure the remaining 1/2 tsp each cumin seeds and coriander seeds.

Heat 1 tbsp ghee in a small pan over medium heat. Fry the sliced onion, remaining cumin seeds, remaining coriander seeds, and curry leaves until fragrant and golden.

Pour the hot tempering over the cooked rajma. Stir gently to distribute the aromatic ghee.

Chop the coriander leaves leaves and scatter them over the curry. Serve the rajma hot with cooked white rice and butter.