To a food processor or blender, add the onion, garlic, ginger, cilantro, chili pepper and curry powder (remove the seeds from the pepper for less heat). Pulse 5-6 times or until you get a coarse paste, scraping down the sides with a spatula as needed. Add 1-2 tablespoons water to help it come together if needed.
Pat dry the chicken with paper towels. Using a piece of paper towel, grab hold of the skin on the bottom of each drumstick and pull hard to peel it off.
Using a meat cleaver or heavy knife, cut off the top inch or so of bone from each drumstick. (Note: you can ask a butcher to do this for you.)
Rub the chicken pieces all over with the curry paste. Optional: Marinate for 10 minutes up to one hour covered in the fridge (see note).
Place a large skillet or heavy-bottomed pot over medium-high heat. When hot, add the oil and chicken pieces one-by-one. Fry for 1-2 minutes and add the broth or water. Once it boils, reduce heat to low and simmer partially covered for 30 minutes. Add a little more water if the sauce gets dry.
Check the chicken and boil uncovered for 10 minutes to thicken the sauce slightly if needed. Garnish with the optional cilantro and green onion before serving.