Rajma (Punjabi Red Kidney Bean Curry)

Heat the oil or ghee in a medium heavy-bottomed pot over medium heat. Add the cumin seeds and let sizzle for 15-20 seconds until fragrant.
Add the chopped onion and cook, stirring often, for 8-9 minutes until deep golden brown; this long saute builds the deep base flavor rajma is known for.
Stir in the ginger-garlic paste and cook for 30-45 seconds, stirring constantly, until fragrant and no longer raw-smelling.
Add the pureed tomatoes and cook for 8-10 minutes, stirring occasionally, until the mixture thickens noticeably and the oil starts to separate visibly at the edges of the pan.
Add the ground coriander, cumin, turmeric, and chili powder. Stir constantly for 20-30 seconds to toast the spices in the thick tomato base, adding a splash of water if it looks like it's sticking.
Add the drained kidney beans and stir well to coat them evenly in the masala.
Pour in the water and salt, and bring to a boil. Reduce heat to low, cover partially, and simmer for 18-20 minutes, stirring occasionally.
Using the back of a spoon, mash about a fifth of the beans against the side of the pot to naturally thicken the gravy.
Continue simmering uncovered for 5 more minutes to reach a thick, hearty consistency that coats the back of a spoon.
Stir in the garam masala and butter if using, and taste to adjust salt.
Garnish with fresh cilantro and serve hot over steamed basmati rice, which is the traditional pairing for this dish.