Grind ⅓ cup of chopped cilantro stems, 7 garlic cloves, 2 teaspoons of cumin seeds, ¼ teaspoon of black peppercorns, and 1 piece of ginger, 1in / 2.5cm long, to a coarse paste.
Chop 275g of ripe tomatoes and blend them to a smooth purée.
Heat 1 tablespoon of oil in a saucepan. Add ½ teaspoon of mustard seeds and let them pop, then add ½ teaspoon of urad dal, 1 dried red chili, and 1 pinch of asafoetida.
Add 10 curry leaves, the spice paste, and ¼ teaspoon of turmeric, and stir until fragrant.
Add the tomato purée, 1½ cups of water, and salt. Simmer over medium-low heat for 9-10 minutes, stirring now and then, until the raw tomato smell is gone. Stir in 2 tablespoons of chopped cilantro.
