Foolproof chicken curry

Heat butter in a large cast-iron pot and sauté onions over medium heat until they have been reduced to a caramelised, sticky jam. Take care not to burn them.
Add whole spices (cinnamon, cardamom,coriander seeds, cumin seeds, cloves,mustard seeds) and cook for a few minutes.
Add the garlic and ginger mix and the leaf masala/curry powder and give a good stir.
Add the browned chicken pieces and stir.
Cook for 5 minutes and then add the tinned tomatoes. Stir quickly and add chicken stock.
Add sultanas and curry leaves and cover with a tight fitting lid. Cook in the oven at 150°C for 2 hours. Check liquid level periodically and add more chicken stock if necessary.
When done, chicken should fall off the bone.
Sprinkle garam masala and fresh coriander on top and give one stir.
Serve with basmati rice and sambals and poppadums.