Brown the Chicken: Heat 1 tbsp oil in a large deep skillet over medium-high heat. Add the chicken breast cubes in a single layer and sear for 3 to 4 minutes without moving until a golden crust forms on the bottom. Flip and cook for 1 to 2 more minutes until no longer pink outside (chicken will finish cooking in sauce). Transfer to a plate.

Build the Aromatic Base: Reduce heat to medium. Add 1 tbsp butter and the diced onion to the skillet. Sauté for 4 minutes until soft. Add the ginger-garlic paste and cook for 60 seconds until fragrant.

Bloom Spices: Stir in garam masala, cumin, coriander, Kashmiri chili powder, turmeric, and salt. Stir constantly for 30 seconds to bloom the spices in the warm fat.

Simmer Tomato Gravy: Add the tomato puree, chicken broth, and sugar. Stir well and bring to a simmer. Cook uncovered for 5 minutes, stirring occasionally, until the sauce thickens and reduces.

Temper the Greek Yogurt (Crucial Step): Turn heat to low. Spoon 3 to 4 tablespoons of the hot tomato sauce from the skillet into the bowl of room-temperature Greek yogurt. Whisk vigorously until smooth and warm. (This gradual temperature equalization prevents the yogurt from breaking or curdling).

Combine & Finish: Pour the tempered yogurt mixture into the skillet, stirring constantly until fully integrated into a silky orange-red sauce. Return the seared chicken and any resting juices to the pan.

Simmer on low for 3 to 4 minutes until the chicken reaches an internal temperature of 165°F (74°C). Do not let the sauce boil rapidly once yogurt is added. Remove from heat, stir in crushed kasuri methi, garnish with cilantro, and serve over basmati rice, cauliflower rice, or with warm naan.