Directions

1. Make garam masala: Gently toast the spices in a dry saute pan over medium heat until they are fragrant. Let cool slightly, then grind spice to a fine powder in a spice grinder or clean coffee grinder. You should have about 1/4 cup.
2. Prepare paste: Puree the onions, garlic, and ginger in a blender until smooth. Set a Dutch oven or other heavy pot over medium heat. When it is hot, add the oil, cumin seeds, and mustard seeds and stir constantly with a wooden spoon until mixture is fragrant and starts to turn golden brown, and mustard seeds begin to pop, 30 to 60 seconds. Stir in onion paste and cook until caramelized, about 45 minutes. During this time, you'll need to stir only occasionally in the beginning, but as the moisture evaporates you'll need to stir more and more frequently and, at the end, fairly constantly to keep it from turning too dark. Once the paste is ready, stir in the garam masala and tomato paste and continue cooking and stirring for another 5 minutes.
3. Pour in the stock and deglaze pot, stirring vigorously to incorporate the paste mixture. Add turmeric, curry leaves, bay leaves, and ground chiles, and season with salt. Bring to a boil, then reduce to a simmer and cook, stirring occasionally, until the stock has reduced slightly (and the flavors have melded), about 45 minutes. Add the chicken and potatoes. Submerging them in the liquid as much as possible. Simmer until the chicken is tender (but not falling off the bone) and cooked through (prick the meat to make sure the juices run clear) and the potatoes are tender (they should still hold their shape but offer little resistance when pricked with a sharp knife). This will take about 30 minutes more.
4. Serve: Add the chopped cilantro and stir to combine. Garnish stew with cilantro sprigs, and serve with rice, yogurt, and lime wedges as desired.