Roasting tin chicken tikka masala

Name: Roasting tin chicken tikka masala
Ingredients: 4 large chicken legs; 1 tsp rapeseed oil; 2 large garlic cloves; 1 onion, roughly chopped; thumb-sized piece of ginger, peeled and roughly chopped; 1 red chilli, roughly chopped; 2 tbsp ghee or butter; 2 tsp ground turmeric; 2 tsp garam masala; 2 tsp ground coriander; 2 tsp ground cumin; 4 tbsp tomato purée; 4 cardamom pods, bashed with the end of a rolling pin; 2 x 400g cans chopped tomatoes; 200ml chicken stock; 1 tsp caster sugar; 100ml double cream; ½ bunch of coriander, finely chopped; ½ red onion, finely chopped, to serve; cooked pilau rice and naans, to serve