Heat coconut oil in large heavy bottom pot oven over medium heat. Season chicken with salt and pepper. Working in batches, cook chicken, until golden brown, about 8-10 minutes. Flip and cook another, 5 minutes. Remove the chicken from the pot and transfer to a plate.
Add onion, garlic, and ginger to the pot and cook, stirring occasionally until onion is very soft and golden brown, about 8-10 minutes. Add tomato paste, garam masala, cumin, turmeric, coriander, cayenne, and cardamom and cook, stirring often, until tomato paste begins to darken, about 4 minutes.
Add the chicken back to the pot. Add the broth, tomato purée, and coconut milk (or cream) to pot. Season the dish with salt and pepper. Bring to a boil, reduce heat, and simmer, partially covered, skimming occasionally if needed, until chicken is almost falling off the bone and liquid is slightly thickened, about 1 1/2 to 2 hours.
Add the sweet potatoes to the pot and cook, partially covered, until potatoes are fork-tender, chicken is falling off the bone, and liquid is thick enough to coat a spoon, about another 30-45 minutes. Remove skin and bones from chicken, if desired, and lightly shred the chicken. Add the chicken back to the pot and season the stew with more salt and pepper.
Divide the stew among bowls and serve with rice and [warm naan | https://www.halfbakedharvest.com/homemade-naan-step-step-photos/]. Dollop each bowl with greek yogurt and garnish with fresh mint and cashews if desired.