In a medium (3-quart) saucepan set over medium, heat HOW MUCH OF THE oil, drippings or butter. When hot, add the onion and cook, stirring regularly, until it is soft and beginning to caramelize, about 7 minutes. Add the adobo and stir for one minute, then add the tomatoes and 1 cup water. Lower the heat and simmer until the mixture has the consistency of tomato paste, about 20 minutes. Scrape the sauce into a blender or food processor and process until smooth. Pour the sauce back into the pan and stir in the vinegar, agave nectar or sugar, Worcestershire and a generous ¼ teaspoon salt.
Heat the oven to 325 degrees. Set a Dutch oven over medium-high heat and film with the HOW MUCH oil. Sprinkle the meat with salt, place in the hot oil and sear all sides to a rich golden brown—this will take about 10 minutes. Return the sauce to the pan and add 1 cup of water. Cover the pot and slide into the middle rack of the oven. Cook until the meat is so tender that it’s nearly falling apart, about 2-2 1/2 hours.