Soak the kidney beans for about 6-8 hours or overnight with 1/2 teaspoon salt.
Stovetop pressure cooker - Rinse the soaked kidney beans and pressure cook it over medium heat it with 3 cups of water and 1/2 a teaspoon of salt (Approximately till the vent or whistle goes off 4 times). Set it aside to cool.
Instant Pot - Rinse the soaked kidney beans and pressure cook it over high for 25 minutes with 3 cups of water and 1/2 a teaspoon of salt. Allow the pressure to release naturally.
Making the gravy (start this process as the kidney beans are being pressure cooked)
Heat oil in a wok over medium heat. If using an Instant Pot, add oil and select the saute function and set it to 'Normal'.
Add the whole spices - black cardamom and bay leaf. Let it fry for about 30 seconds.
Add the chopped onions. Fry the onions till they turn soft and translucent (approximately 10 minutes)
Add chopped green chilies along with ginger and garlic. Fry them for a minute or two to let the raw taste disappear.
Add chopped tomatoes, along with the spice powders - chili, cumin, and coriander powder. Mix well.
Continue to cook till the tomatoes begin to soften.
[Optional step] Add about a cup of liquid from the cooked rajma. Use an immersion blender, and blend the onion-tomato mixture to a fine paste. [This gives the gravy a creamy texture].
Add the cooked kidney beans with the liquid along with garam masala and dry mango powder (if using).
Let the rajma simmer for about 10 minutes. For best results, simmer for 30 minutes.
Serve with either chapatis or steamed rice.
Add a teaspoon of store-bought Rajma masala - gives this dish a nice tang.
To make it a one-pot meal,
Prepare the gravy first and then add soaked beans to it.
Pressure cook the beans with the gravy for about 30 minutes using an Instant Pot.
Note - The reason I don't pressure cook kidney beans with the gravy because the results are inconsistent. The beans don't cook uniformly (at times) and often take longer to cook. This is because tomatoes are acidic and they interfere with the cooking of the beans.