Add the remaining mustard oil to the cooking pot and let heat up.
Temper the hot oil with bay leaf and cinnamon sticks to temper the hot oil, followed immediately by the chopped onions.
Cook the onions, stirring regularly, until they turn golden brown (but not too dark), about 6-8 minutes.
Next, add the ginger paste, garlic paste, pureed tomato, red chili powder and turmeric powder.
Mix and cook the tomatoes for 3-4 minutes or until you see the oil beginning to seperate.
Lower the heat to low medium and wait for a minute. Sprinkle the remaining bhuna masala powder over the cooked tomatoes. Then, add the marinated chicken, making sure to scrape any remaining marinade from the bowl into the pot.
Toss the chicken to combine it well with the onions & tomato masala. For the next 5-7 minutes, bhuno the chicken with the masala on medium heat. You will see that the chicken starts releasing its juices.
Reduce heat to low and add the whisked yogurt. Immediately stir the chicken to mix with yogurt and keep stirring continously for next 2-3 minutes or until the yogurt has warmed through. This prevents the yogurt from curdling.
Bump up the heat to medium. Keeping it on low will cause the chicken to release excess moisture, preventing a proper bhunai (sautéing) and the sauce getting watery.
In about 3-4 minutes, the yogurt will start releasing its water. When you see that there is enough liquid in the cooking pot, cover it with a lid. Reduce heat to low medium once you cover.
As the chicken will cook,it will release its own juices plus water from yogurt will is enough to cook it. Do not add water. You will need to check and stir in between once or twice. It takes about 12-15 minutes for the chicken to cook fully (cooking time depends on cut and variety of chicken, please adjust as needed).
Uncover once the chicken is fully cooked. A visual indicator of chicken doneness is that the chicken flesh will pull away from the drumsticks.
Bhuno (fry) the chicken on medium heat for another 5-6 minutes to dry out the liquid further and bring out the best bhuna flavor. You will see a layer of oil and a thick masala in the cooking pot.