Combine all the marinade ingredients and coat the chicken breasts. Leave for 30 minutes to marinade in the fridge.
Meanwhile, melt the butter in a large pan over a medium heat and soften the onion in it for 20 minutes, until golden brown and completely soft. Add the ginger and garlic, then stir through the chopped tomatoes with the smoked paprika, fenugreek, garam masala, chilli powder and tomato purée. Add 300ml water and simmer for 20 minutes, until thickened.
Heat a pan with the vegetable oil. Add the chicken pieces and fry for 5-6 minutes until brown all over. You may need to do this in two batches.
Add the browned chicken to the curry sauce and simmer for 10 minutes with the lid on. Stir through the yogurt and coriander. Meanwhile, cook the rice according to the instructions on the packet. Serve the chicken with the basmati rice.