Heat the oil in a large, heavy-based casserole dish and brown the drumsticks evenly for 5–6 minutes. Remove with a slotted spoon and set aside.
Add the onion and stir-fry over a low heat for 10 minutes. Add the garlic, lemon grass, chilli and curry paste and stir-fry for 1–2 minutes.
Return the chicken to the dish with the palm sugar and stock. Bring to the boil, season and cover tightly. Cook in a preheated oven at 140°C (275°F), Gas Mark 1 for 1½–2 hours or until tender. Remove from the oven and serve immediately.