Brisket at its best is meltingly tender with deep, beefy flavor. But it has a reputation as a finicky cut that can end up dry and tough, especially the leaner flat end that's sold in most markets. The secret to succulent results starts with low, moist heat. A slow braise breaks down tough muscle fibers and connective tissue. The post-braising process is just as important: The braised brisket rests overnight in the cooking liquid. This gives the meat a chance to relax and reabsorb any juices pushed out as it cooked. The fat cap stays on the brisket while it cooks as an extra guard against dryness. It is carved off before reheating, and the overnight chill lets any rendered fat rise to the top of the cooking liquid and solidify, so it can be removed easily. Finally, the meat is sliced and reheated in the rich, meaty cooking liquid to guarantee that every bite is juicy. The liquid is then used in a sweet onion jam.