Preheat your oven to 400°F (200°C) and line a baking sheet with aluminum foil for easy cleanup.

In a blender or food processor, combine the onion, garlic, ginger, lemongrass, chili powder, turmeric, cumin, and coriander into a smooth spice paste.

Heat the vegetable oil in a saucepan over medium heat. Add the spice paste and sauté for 5-7 minutes until it becomes fragrant and the oil starts to separate.

Pour in the coconut milk, brown sugar, salt, and tamarind paste. Simmer gently for 5 minutes until the sauce thickens slightly, then remove from heat.

Place the chicken pieces on the prepared baking sheet. Pour about half of the sauce over the chicken, rubbing it thoroughly into the skin.

Bake for 30 minutes in the center of the oven.

Remove the tray, baste the chicken generously with the remaining sauce, and return to the oven.

Bake for another 10-15 minutes. In the final 5 minutes, switch the oven to 'broil' to char the skin and caramelize the coconut sauce slightly (watch closely to prevent burning).

Let the chicken rest for 5 minutes before serving with steamed rice.