Cover with aluminum foil and bake at 320 degrees for two hours.
Remove the meat and check the internal temperature. Corned beef must be at least 145 degrees for safe eating, but collagen and fat do not begin to dissolve until the temp reaches 190 degrees. The meat is safe to eat, but needs more time to tenderize.
At this time you may find that the fat cap is beginning to shrink, causing the meat to curl. Use a sharp knife to cut through the fat cap from side to side in a couple of places. This should release the fat, allowing the beef to maintain a flat shape. Keep the fat cap in place, just score it. You will remove it later but for now it will keep the meat from drying out.
Flip the meat with the fat cap down, cover with foil and return to oven. Continue checking for desired tenderness every 10-15 minutes.
Remove from oven to a cutting board when tender and discard liquid.
Use a sharp knife to remove the fat cap. Discard the fat cap.
Cut a small piece of meat off the end and taste for saltiness. Oftentimes the meat will be too salty for your liking at this point.
If the meat is too salty, bring enough water to almost cover the corned beef to a slow boil in a saucepan over medium heat. Place the corned beef in simmering water for 5 minutes. Take the meat out and taste again. If it is still too salty, return it for another five minutes.
If perfect, allow to cool before slicing. To get perfect tender slices you need to slice AGAINST the grain of the meat.
Notice the way the grain of the meat runs in the picture. You will see that when I slice it, I slice it against the grain, not in the direction of the grain.