Using a mortar and pestle, pound the garlic and ginger to a smooth paste.
Heat the oil in a large frying pan over a medium heat. Add the onions, curry leaves, chilli and cracked peppercorns. Cook for about 15 minutes, stirring often, until the onions are golden.
Reduce the heat to medium-low, then add the garlic-ginger paste. Cook for 5 minutes, stirring now and then. Stir in the coriander seeds, turmeric and a little salt, and cook for another 5 minutes.
Add the chicken to the pan, give it a stir, then add the water and garam masala, mixing well. Cover and cook gently for 5 minutes or until the chicken is cooked through. Stir in the freshly ground pepper just before serving.