Heat butter in large pan over a gentle heat and cook onion, garlic & ginger until soft and golden.
Add the curry powder and mustard seeds and cook for further 3-4 minutes. Add salt and the vinegar and stir well.
Increase the heat slightly and add the meat and tossing it to coat well.
Add chilli and tomatoes and bring to the boil, then lower heat to a simmer.
Cover the pan and cook for an hour, stirring occasionally until the meat is tender.
If you have too much juice remove the meat and cook on high till it is reduced.
Garnish with slivered lightly toasted almonds.
Serve with rice and naan bread