Named after its dark, sweet sauce, posta negra is a classic Colombian dish made by braising beef in a flavorful liquid seasoned with panela sugar and spices. For our version, we call for a 5-pound beef chuck roast; it's a fat-rich cut, so trim it well before tying the roast. In the end, the meat will be superbly tender and succulent. In Colombia, the dish might be served with fried plantains, yucca fritters and a simple salad; we liked this rich beef with an easy pico de gallo and/or mashed potatoes.