Cut the chicken into serving pieces and toss the onions over it. Let stand for 30 minutes. Melt butter in a heavy pan and stir in coriander, salt, turmeric and chili powder. Add the chicken and onion and brown lightly. Add about 1/3 cup water and cover tightly. Reduce heat and let simmer for 40 minutes or until chicken is tender. Stir in the juice just before serving.