These big, thick ribs offer a tender beef experience that's akin to braised brisket but packed with slow-cooked barbecue flavor. Note that these are knife-and-fork ribs, not finger food.
In a small bowl, combine mustard, sugar, chile powder, cumin, paprika and salt. Sprinkle the mixture all over the ribs, rubbing it in with your fingers, and set aside for at least 20 minutes, or cover and refrigerate for up to 1 day.
Preheat oven to 275 degrees. Cover a large baking sheet with aluminum foil and place the ribs on it. Bake in the middle of the oven until the ribs are fork-tender and the meat has shrunk away from the ends of the bones, about 2 hours.
When ribs are tender, prepare a grill for medium-heat cooking. Mix the barbecue sauce with a tablespoon or two of water (this will make basting easier). Place the ribs on the grill and cook, turning them and basting them frequently with the sauce, until well browned and nicely glazed, about 15 minutes. (Be careful not to let the sauce burn; move the ribs to a cooler area of the grill if they begin to char.) Transfer to a platter and serve.