Chicken tikka masala

Name: Chicken tikka masala
Ingredients: 4 skinless, boneless chicken breasts; 4 tbsp readymade tandoori paste; 2 tbsp natural yoghurt; 3 tbsp vegetable oil or ghee (clarified butter); 1 cinnamon stick; 8 cardamom pods; 1 large onion, finely chopped; 3cm/1¼in piece of fresh ginger, peeled and grated; 2 garlic cloves, crushed; 1 tsp ground cumin; 1 tsp ground coriander; ½ tsp turmeric; ½-1 tsp cayenne pepper (depending on how hot you like it); 1x200g can chopped tomatoes; 150ml/5fl oz chicken stock or water; 1½ tsp garam masala; ½ lemon, juice only; ½ tsp salt