Heat oil in a heavy-based pot over medium-high heat.
Add onions and braise over medium heat until a light golden colour.
Add the curry leaves, cardamom, cloves, allspice and cinnamon fry for about 20 seconds.
Add ginger and garlic paste, spices and salt and stir through for about 20 seconds
Add the tomatoes with a bit of water and stir fry for a few minutes or until the tomato is soft and mushy.
Add chicken and turn to coat in spicy tomato gravy, for 10 minutes.
Lower the heat slightly and add a 1/2 cup of water and simmer gently for approx 10 mins.
Add the potatoes and another 1/2 cup of water and continue to simmer for another 10 mins or until the potatoes are completely soft.
If you prefer a thinner gravy add a little more water and adjust the salt.
Just before serving add half a teaspoon of garum masala and some chopped coriander.
Serve hot with rotis or rice and sambals.