Cool, then transfer leftovers to containers. Freeze for up to two months, defrost in the fridge and reheat well before eating.
Put the drumsticks in a large bowl with 1 tbsp oil, the garlic, ginger, garam masala, turmeric and 2 tbsp yogurt. Toss together with your hands until coated. Leave to marinate for at least 30 mins (can be left in the fridge overnight). Heat oven to 180C/160C fan/gas 4.
Put the potatoes in a large roasting tin with the remaining oil and plenty of seasoning. Add the chicken drumsticks and bake for 40-45 mins until cooked and golden.
Scatter the tomatoes, onion, coriander and some seasoning over the chicken and potatoes, with the remaining yogurt served on the side.