Lightly roast the cumin seed and coriander seed by frying with no oil for a minute or so, stirring constantly. Grind these and combine them into a paste with the other spices, the garlic, ginger and the vinegar. Add the lamb to the marinade and mix well. Refrigerate for 3-24 hours while mixing every few hours as convenient.
2.
Finely chop the onions and potatoes and saute them for 5 minutes in the butter.
3.
Add lamb and spice paste and simmer over low heat for half an hour. The marinating does add a lot of flavor and makes the meat much more tender. This can be skipped if need be.
NOTES:
* A spicy hot Indian lamb dish -- Very loosely based on Dharamjit Singh's recipe in "Indian Cookery: A Practical Guide." Most restaurants that serve this dish pronounce it vinDAloo, with the stress on the second syllable.
