1/4 cup canola oil
5 fresh curry leaves
4 cups thinly sliced yellow onion
2 Tbs. finely chopped garlic
2 Tbs. finely chopped ginger
2 whole Thai green chilies
4 Tbs. tomato paste
2 Tbs. cumin
1 Tbs. coriander
2 tsp. Kashmiri chili powder (or 1 tsp. cayenne pepper)
2 tsp. ground turmeric
2 tsp. cinnamon
1 tsp. cardamom
1 tsp. crushed red pepper flakes
1/2 tsp. ground fennel
1 Tbs. kosher salt
2 cups water
2 ½ lbs. boneless, skinless chicken thighs, cut into 1-inch pieces
1/4 cup coconut milk
Make the chili paste: Heat the oil in a large pot over medium heat until it shimmers. Add the curry leaves and cook until they start to sizzle. Add the onions and cook, stirring frequently, until translucent, about 10 minutes. Stir in the ginger, garlic, and chilies and cook, stirring frequently, until the garlic starts to brown, about five minutes. Stir in the tomato paste, spices, and salt and cook for about five more minutes. Transfer the mixture to a blender, add the water, and puree well.
Transfer the curry paste back to the pot and add the chicken and coconut milk. Bring to a simmer, cover, reduce the heat to low, and simmer for 45 minutes, stirring occasionally. Season with additional salt if desired.