Marinate the beef with vinegar, tamarind paste, minced garlic, grated ginger, and salt. Cover and refrigerate for at least 120 minutes.
Blend the marinated beef with cumin seeds, coriander powder, turmeric powder, black pepper, and green chilies until smooth.
In a pot, heat oil and sauté onions and mustard seeds until golden brown. Add the Vindaloo paste and cook for 5 minutes.
Add the marinated beef to the pot, stir, and cook for 5-7 minutes until browned.
Add water to cover the beef, bring to a boil, then reduce heat and simmer for 90-120 minutes until tender.
Taste and adjust seasoning. Simmer uncovered for a few more minutes if a thicker sauce is desired.