Heat the oil in a Dutch oven or a deep, wide saucepan set over medium-high heat. Add the onions and stir to coat them with the oil. Spread them in an even layer and cook for 2 min. Stir well, rearrange in an even layer again, and cook for 2 min.; the onions should have begun to brown at the edges. Reduce the heat to medium and cook, stirring occasionally, until the onions are a rich brown, another 10 to 12 min. Lower the heat if necessary so the onions caramelize but don’t burn.
Meanwhile, put the yogurt in a small bowl, stirring until it’s creamy. Add the cornstarch and mix well.
Add the ginger, garlic, and chiles to the onions. Cook over medium heat, stirring frequently, for 2 min. so they meld with the onions. Add all the chicken thighs and cook, stirring occasionally, until they lose their raw color and begin to brown, 5 to 6 min. Lower the heat to medium low and add the coriander, cumin, turmeric, and cayenne. Cook for 2 min., stirring frequently and scraping the bottom of the pan.
Add the tomatoes and their juices, the yogurt mixture, the chopped cilantro, and the salt. Stir well, cover with a tight-fitting lid, and bring to a boil. Lower the heat and simmer until the chicken is cooked through, 20 to 25 min. Remove from the heat and taste for salt.
To serve, sprinkle on the garam masala, transfer to a serving dish, and garnish with more chopped cilantro.
Make Ahead Tips
You can freeze this curry, in which case you shouldn’t add the garam masala and cilantro garnish until you're ready to serve. Thaw the curry in the fridge and reheat over low heat. Then sprinkle with the garam masala and a little ground cumin, cover, and let sit for a few minutes to let the aroma infuse the curry. Transfer to a serving dish and sprinkle with the chopped cilantro.
nutrition information (per serving):
based on six servings, Calories
11, Fat Calories
100, Saturated Fat
32, Monounsaturated Fat
15, Polyunsaturated Fat