1. Marinate the Chicken

In a large bowl, combine the yogurt, vinegar, turmeric powder, ground cumin, and salt. Add the chicken pieces, ensuring they are well coated with the marinade. Cover the bowl and refrigerate for at least 30 minutes, or up to 2 hours for deeper flavor.

2. Prepare the Spice Base

While the chicken marinates, toast the mustard seeds, fenugreek seeds (if using), and dried red chilies in a dry skillet over medium heat for 1–2 minutes, until fragrant. Remove from heat and set aside.

3. Cook the Aromatics

Heat the oil or ghee in a large pan or Dutch oven over medium heat. Add the finely chopped onions and sauté for 8–10 minutes until golden brown. Add the minced garlic and grated ginger, cooking for an additional 1–2 minutes until fragrant.

4. Add the Ground Spices

Lower the heat slightly and add the ground cumin, coriander, paprika, chili powder, cinnamon, and turmeric powder. Stir well to coat the onions and toast the spices for about 1 minute to release their aroma.

5. Incorporate the Tomatoes

Add the chopped tomatoes to the pan and cook for 6–8 minutes, stirring frequently, until the mixture thickens into a paste.

6. Add the Chicken

Add the marinated chicken pieces to the pan, stirring to coat them in the spice mixture. Cook for 5–7 minutes until the chicken begins to brown.

7. Simmer the Curry

Pour in the coconut milk (or water) and add the toasted whole spices, vinegar, and sugar (if using). Stir to combine. Bring the curry to a gentle boil, then reduce the heat to low. Cover and simmer for 20–25 minutes, stirring occasionally, until the chicken is tender and the sauce has thickened.

8. Finish with Garam Masala

Stir in the garam masala during the final 5 minutes of cooking for added depth and fragrance. Taste and adjust the seasoning with salt, vinegar, or chili powder as needed.

9. Serve

Garnish with fresh cilantro and serve hot with steamed basmati rice, naan, or roti.