Heat oil in the dutch oven/skillet/cooking pot. Add ginger and garlic. [Note: We add this first so that they get enough time to fry in oil to turn aromatic. Turn the heat to medium low if you notice browning. ]
Now add the sliced onion and cook until they turn translucent. Add the green chillies. [Note: Turn the heat back up to medium if you had reduced it in the previous step]
Add the spice powders and fry until aromatic. [Note: This is the key to a best-tasting chicken curry. The spice powders should be roasted well without burning. Reduce the heat if you think the spices are burning.]
Add tomatoes and cook until they turn soft and oil leaves the sides.[Note: Turn the heat back up to medium if you had reduced it in the previous step]
Add the chicken pieces and stir well to coat the pieces with onion, tomatoes & spice mixture. Cook uncovered for 1 minute or two. Add salt. Mix well. [Note: Start with approx.¾ teaspoon of salt. Then once the chicken is cooked, taste and add more if needed]Cover & cook until the chicken pieces are cooked through and are tender. Stir occasionally. Chicken takes about 25-30 minutes to cook.
While the chicken is cooking, grind the coconut and cashew nuts with about ¼ -½ cup of water to a smooth paste.
Once the chicken pieces are cooked well, add coconut paste and curry leaves. Bring to boil & remove from heat.