Make the bharta. Heat the 1 1/2 TBSP oil in a medium frying pan over medium-high heat. Once hot, add cumin seeds and cook for 1 minute, tossing or swirling frequently to prevent burning. Add the onions with a pinch of salt and cook for 4 to 5 minutes, but don’t let them brown. Add the garlic, ginger, serrano peppers, and turmeric, and cook, stirring frequently for 60 to 90 seconds. Add the coriander, salt, and tomatoes, and cook until the oil starts to release from the tomatoes and the tomatoes are soft, about 5 minutes.