Warm vegetable oil in a large pot over medium heat. Season chicken with salt and pepper and place skin side down in the pot. Cook until golden brown without turning, 8-10 minutes. Transfer chicken to a plate.
To the same pot, add onion, garlic and ginger. Cook, stirring occasionally, until onion is soft and golden brown, about 8 minutes. Add tomato paste, garam masala, cumin, turmeric, coriander, cayenne pepper and cardamom. Cook, stirring often, until tomato paste begins to darken, about 4 minutes.
Nestle the seared chicken in the pot and pour the chicken broth, tomato purée and half-and-half on top. Season with salt and pepper, stir gently and bring to a boil. Reduce heat and simmer, partially covered, until chicken is almost falling off the bone and liquid is slightly thickened, about 1 hour. Remove the chicken from the pot and let cool slightly. Discard the skin and bones, shred chicken into bite-sized pieces and return chicken to pot.
Add the potatoes and cook, partially covered, until they are fork tender and the sauce is thickened, 35-45 minutes. Stir occasionally to ensure the sauce hasn’t thickened too much and potatoes aren't sticking to the bottom of the pot. If sauce is too thick, thin with a bit of chicken broth.
Sprinkle cilantro over stew, and serve with a dollop of Greek yogurt and warm naan or steamed rice.
Notes
*If you can't find tomato purée, whir canned diced tomatoes in a food processor or blender until smooth. **For a richer flavor, use heavy cream.
Recipe by Two of a Kind at http://www.twoofakindcooks.com/indian-spiced-chicken-stew/