
Heat the vegetable oil and butter in a large, lidded casserole on the hob. Add the onions and a pinch of salt, cooking for 15-20 minutes until soft and golden.
Add the chicken tikka masala paste and red peppers, cooking for an additional 5 minutes to cook out the rawness of the spices.
Add the chicken breasts, stirring well to coat in the paste. Cook for 2 minutes, then add the chopped tomatoes, tomato purée, and 200ml water. Cover with a lid and gently simmer for 15 minutes, stirring occasionally, until the chicken is cooked through.
Remove the lid and stir through the mango chutney, double cream, and natural yogurt. Gently warm through and season to taste. Set aside any portions you wish to freeze.
Scatter with chopped coriander and serve with basmati rice and naan bread.