1 (2 1/2 to 3 pound) chuck roast
4 medium size tomatoes
1 small onion
1 bunch very fresh cilantro
1 clove garlic
1 tablespoon cumin
1/2 teaspoon chili powder
1/4 cup vinegar
Cut the roast into 1/2-inch cubes.
Put it in a large frying pan, pour on the vinegar and let it brown slowly. Add water to keep the meat from drying as it browns.
Cut the tomatoes, tomatillo and onion into quarters and add to the frying pan. Crush the clove of garlic and add to the pan, along with the chili powder and cumin. Use about half of the cilantro. Chop the leaves and add to the pan. Let the dish simmer for at least 1 hour. The longer it simmers, the better it is. Add small amounts of water if needed to keep liquid in the pan. Salt and pepper to taste.
Serve with warm tortillas, guacamole and sour cream.