Add the chicken, Greek yogurt, lemon juice, olive oil, and all of the chicken seasonings to a bowl. Mix until the chicken is evenly coated. Cover and refrigerate for at least 1 hour, although overnight is best for maximum flavor.

Heat a skillet over medium-high heat. Once hot, add the marinated chicken in a single layer, making sure not to overcrowd the pan. Sear for about 2–3 minutes on each side, or until browned and nearly cooked through. Remove the chicken from the pan and set aside.

Reduce the heat to medium and add the butter to the same pan. Use a wooden spoon or spatula to scrape up the browned bits as the butter melts.

Add the diced onion and sauté for 5–7 minutes, stirring occasionally, until softened and lightly golden. Add the garlic and ginger and cook for another minute, until fragrant.

Add all of the masala spices and the curry powder, if using. Stir continuously for about 30 seconds, allowing the spices to become fragrant without burning.

Pour in the tomato purée and water, stirring well to combine. Reduce the heat to medium-low, cover, and simmer for 15 minutes, stirring occasionally.

For a smooth masala, use an immersion blender to blend the sauce until smooth, then pass it through a fine-mesh sieve. This step is optional, but highly recommended for a silky sauce.

Return the sauce to the pan and reduce the heat to low. Stir in ¼ cup heavy cream, adding up to another ¼ cup if you prefer a richer, creamier sauce.

Add the seared chicken and any juices from the plate back into the sauce. Crush the dried fenugreek leaves between your palms to release their aroma, then add them to the pan. Stir gently to coat the chicken.

Cover and let the chicken simmer gently over low heat for about 5 minutes, or until completely cooked through and the sauce has thickened to your desired consistency. Taste and adjust the salt or cream as needed.

Serve hot with basmati rice or naan. Finish with additional dried fenugreek leaves and an optional drizzle of cream.