Let the marinating roast sit at room temperature for an hour before cooking
Place a large skillet or Dutch oven over medium low heat
Crumble 2 ounces of piloncillo into the skillet and let it warm undisturbed until it begins to caramelize
While the piloncillo is warming, transfer the roast out of the marinade (set the marinade aside for now) and dry it with paper towels
Carefully place the roast into the caramelized piloncillo and reduce the heat to low
Cook the beef, turning every 30 seconds or so, until it the entire roast is deeply browned and the piloncillo is dark and sticky
Add the marinade, 1 large sliced yellow onion, 1 large sliced sweet bell pepper, 2 diced roma tomatoes, 6 cloves of minced garlic, 2 bay leaves, 1 tablespoon of fresh oregano leaves and a big pinch of salt and black pepper and stir to combine everything
Cover the skillet and simmer over low heat for 3 1/2 - 4 hours or until the beef is tender