Take 2-3 tbsp of the curry paste and smear all over the turkey drumstick, rubbing it well into the flesh and under the skin. Cover and leave in the fridge to marinate for a couple of hours or longer, if you have the time.
When ready to cook, preheat the oven to 180°C/gas mark 4 and place the marinated drumstick on a baking tray. Cover with foil and roast for 1hr & 30mins to 1hr & 45mins hr, until cooked and the juices run clear. 15 mins before the end of cooking, remove the foil, and return to the oven, to let the meat brown.
Meanwhile, use the remainder of the jar of curry paste to make a sauce:
Heat the oil in a sauté pan. Add the onions and garlic, cover and sweat for 4-5 mins, stirring occasionally until softened.
Stir in the ginger, then add the remaining curry paste (about half the jar). Stir until well mixed.
Pour in the chopped tomatoes, and milk if using, then bring to the boil and simmer for 10 mins, before serving with the sliced turkey.