Blend the onions, garlic, ginger and chilli in a blender or liquidiser, or chop very finely.
Cut each thigh into 4 pieces, heat the oil in a large frying pan and add the chicken. Cook over a high heat until evenly browned. Remove from pan and place in slow cooker.
Add the butter to the pan and when melted add the onion mixture. Cook over moderate heat for 3 minutes. Add all the spices and cook for a further minute.
Mix in chicken stock, sugar and salt. Bring to the boil and then transfer to slow cooker pouring over chicken.
Cover and cook for 5 - 7 hours on Low (or 3 hours on high).
Add the cream and ground up nuts. Serve with rice and naan bread.