Grind the cumin, coriander, fennel, and black peppercorns in a spice grinder. Mix in the Kashmiri chili powder.
Marinate the chicken thighs with the spice powder for at least 4 hours, preferably overnight.
Heat up cooking oil in a sauté pan over medium heat. Fry the fennel seeds and cinnamon stick for 30 seconds.
Add in the onions. Fry for 15 minutes, occasionally stirring so they brown evenly.
Once the onions have cooked down, add in the garlic, ginger, and curry leaves. Fry for 1 minute.
Turn up the heat to high. Sear the marinated chicken pieces for 4 minutes.
Season with salt. Pour in a 1/4 cup of water to produce a light gravy. Cover. Reduce the heat to low and cook for 15 minutes.