Heat oil and fry onions until soft. Drain the onions, leaving the oil in the pot. Add the spice ingredients and (A). Fry until fragrant and oil rises. Put in the chicken and stir to mix. Pour in half portion of yoghurt and stir thoroughly to mix. Simmer over moderate heat for 20-30 minutes, stirring now and then to prevent chicken from sticking to the base of the pot.
When chicken is tender and gravy is fairly thick, return the precooked onions to the gravy and add in remaining yoghurt. (If a drier curry is preferred, simmer longer, uncovered.) Add salt and sugar to taste.