Put the butter in a casserole or a skillet and turn the heat to medium-high. Put the sugar on a plate and dredge the meat in it until all the surfaces are coated. Reserve the remaining sugar. When the butter foam subsides, brown the meat on all sides--this will take about 15 minutes--seasoning it with salt and pepper as it browns.

When the meat is nicely browned, add the vinegar and cook for a minute, stirring. Add the cranberries and remaining sugar and stir. Strip the zest from the orange (you can do it in broad strips, with a small knife or vegetable peeler) and add it to the skillet. Juice the orange and add the juice also, along with a pinch of cayenne. Turn the heat to low and cover; the mixture should bubble but not furiously.

Cook, turning the meat and stirring about every 30 minutes, for 2 hours or longer, or until the meat is tender. When the meat is done, taste and adjust the seasoning if necessary. Turn off the heat and let the roast rest for a few minutes, then carve and serve, with the sauce.

With Minimal effort: Faster Pot Roast with Cranberries: Substitute a 2- to 3-pound piece of tenderloin (filet mignon) for the chuck or brisket and reduce the cooking time to about 1 hour, or until the internal temperature is 125 to 130 degrees (medium-rare); you can cook it longer than that if you like.