Place the beef in a non-reactive dish.

Place the white vinegar, ground cumin, mustard, onion, scallions, salt and pepper in the blender or food processor.

Rub the onion mixture all over the beef. Let it rest for 2 to 3 days in the fridge.

Heat the oil in a large pot and place the beef and brown, searing it on both sides.

Add the water, bay leaves, thyme and oregano. Bring to a boil, then reduce the heat and simmer about 3 hours or until the meat is very tender.

Take the beef from the pot. Let it rest for at least 15 minutes, tented in aluminum foil to keep warm, before carving to serve.

Meanwhile make the sauce: Add the melao to the pot and mix with the cooking water that is left in the pot from the beef. Mix well and cook for about 2 minutes over low heat. Place the sauce in a blender and blend until smooth and pour on top of the beef. Serve over white rice.