Chicken tikka masala

INGREDIENTS

• 4 tbsp vegetable oil
• 25g butter
• 4 onions , roughly chopped
• 6 tbsp chicken tikka masala paste (use shop-bought or make your own - see recipe, below)
• 2 red peppers , deseeded and cut into chunks
• 8 boneless, skinless chicken breasts , cut into 2.5cm cubes
• 2 x 400g cans chopped tomatoes
• 4 tbsp tomato purée
• 2-3 tbsp mango chutney
• 150ml double cream
• 150ml natural yogurt
• chopped coriander leaves, to serve