Pat the chicken pieces dry with paper towels and season all over with 1/2 teaspoon salt and the black pepper. Drying the chicken is important here because damp chicken will steam in the pan instead of getting that golden sear on the outside.

Heat the oil in a large deep skillet over medium-high heat until it shimmers. Add the chicken in a single layer, working in batches if needed so you do not crowd the pan. Sear for 3 to 4 minutes without moving, until the pieces are golden on the bottom. Flip and cook another 2 minutes. The chicken does not need to be fully cooked through yet. Transfer to a plate and set aside.

Reduce the heat to medium. Add the diced onion to the same skillet and cook, stirring occasionally, for 4 to 5 minutes until softened and starting to turn golden at the edges. Add the garlic and ginger and stir constantly for about 60 seconds until fragrant.

Add the garam masala, cumin, coriander, turmeric, and cayenne (if using) directly to the pan. Stir the spices into the onion mixture and let them toast for 60 seconds, stirring constantly so they do not burn. You will smell them bloom and deepen. This step makes a real difference in the final flavor.

Pour in the diced tomatoes with their juices. Stir well and scrape up any bits stuck to the bottom of the pan. Simmer for 3 minutes, stirring occasionally, until the tomato mixture thickens slightly.

Pour in the coconut milk and add the sugar and remaining 1/2 teaspoon salt. Stir everything together. Nestle the seared chicken and any accumulated juices back into the pan. Bring to a gentle simmer over medium heat.

Simmer uncovered for 10 to 12 minutes, stirring occasionally, until the chicken is fully cooked through (internal temperature of 165 degrees F) and the sauce has thickened to a creamy, spoon-coating consistency. Taste and adjust salt if needed.

Serve over basmati rice and scatter fresh cilantro on top. Warm naan on the side is a great addition if you have it.