In a medium sized bowl, mix together the marinade ingredients. Cut the chicken into bite-size pieces then add to the marinade and toss well to coat. Cover and refrigerate until needed.
Heat the ghee or oil in a large pan over medium heat. Once hot, add the onion, garlic, chilli, ginger and a sprinkling of salt and pepper. Cook until onion is soft, 5-10 minutes.
Add the spices and tomato purée to the pan, mix into the other ingredients and cook for further 2 minutes.
Add the stock, scraping the bottom of the pan with a wooden spatula to lift any stuck bits.
Pour into slow cooker then add the marinated chicken, give it a big stir to combine.
Cook on low for 6 hours.
To serve, sprinkle with flaked almonds and serve with cooked basmati rice and naan bread. You can also serve with mango chutney.