Marinate the Chicken: Combine the chicken pieces in a medium bowl with the whisked yogurt, half a teaspoon of the turmeric, half a teaspoon of the salt, and the Kashmiri chili powder. Toss until every piece is evenly coated in the pale orange marinade. Cover the bowl and let the chicken rest at room temperature for 15 minutes. The acid in the yogurt begins to tenderize the muscle fibers, and the turmeric lends color that will deepen during cooking.
Build the Onion Base: Heat the oil in a large heavy-bottomed pot over medium heat until the surface shimmers, about 2 minutes. Add the diced onion and cook, stirring every 2 minutes, for 15 minutes total until the onion turns a deep golden-brown and smells nutty and sweet. Do not rush this step by raising the heat. A properly caramelized onion base is the structural flavor foundation of the curry sauce.
Bloom the Aromatics and Spices: Push the onion to the sides of the pot and add the garlic and ginger to the cleared center. Cook for 90 seconds, stirring constantly, until fragrant and lightly golden. Add the ground cumin, ground coriander, garam masala, and the remaining half teaspoon of turmeric directly onto the garlic and ginger. Stir everything together and cook at medium heat for 60 seconds until the spices smell toasty and the mixture forms a thick, fragrant paste. Blooming spices in fat rather than liquid releases fat-soluble flavor compounds that water cannot extract.
Add the Tomatoes and Reduce: Add the chopped tomatoes and the remaining half teaspoon of salt to the pot and stir to combine with the spice paste. Cook over medium heat for 8 minutes, stirring occasionally, until the tomatoes fully break down, the oil begins to separate visibly around the edges of the masala, and the mixture darkens to a deep brick-red color. This separation, known as bhunao in South Asian cooking, signals that the raw flavor of the tomatoes has cooked out and the base is ready to receive the chicken.
Sear the Marinated Chicken: Increase the heat to medium-high. Add the marinated chicken pieces to the pot in a single layer, pressing each piece gently into the masala base. Sear without stirring for 3 minutes until the undersides develop a light golden crust and release naturally from the pan. Flip the pieces and sear the second side for 2 minutes. Searing at this stage builds a thin layer of fond on the chicken surface that adds depth to the finished sauce.
Simmer the Curry: Pour the chicken stock into the pot and stir to lift any fond from the bottom. Bring the liquid to a gentle simmer over medium heat, then reduce to medium-low. Cover the pot with a lid and cook for 20 minutes, stirring once at the 10-minute mark, until the chicken reaches an internal temperature of 74°C / 165°F and the sauce has thickened to a consistency that coats the back of a spoon. Taste the sauce and adjust salt as needed before removing from the heat.
Rest and Garnish: Remove the pot from the heat and let the curry rest uncovered for 5 minutes. The residual heat continues to gently cook the chicken while the sauce tightens slightly as it cools. Scatter the fresh cilantro over the top just before serving. Resting also allows the fat to rise and the spice flavors to meld into a more cohesive, rounded sauce.
