Place brisket on a rimmed baking sheet, pat dry with paper towels, and generously season both sides with salt and pepper.
Refrigerate, uncovered (or loosely covered with plastic wrap), for 24-36 hours.
Preheat oven to 350°F.
Allow brisket to come to room temperature for 1 hour.
Lightly coat the bottom of a Dutch oven or baking dish (large enough to hold the brisket and onions) with oil.
Add onions and season with salt and pepper. Place brisket on top of onions.
Oven-sear at 350°F, uncovered, for 30 minutes on each side.
Add broth, soy sauce and brush brisket with silan. Lower the oven temperature to 300°F. Cover brisket and continue cooking at 300°F for about 3 hours or until a fork can be inserted into and removed from the center of the brisket with no resistance.
Carefully remove brisket to a cutting board and let rest for 20 minutes. Cover loosely with foil if you will be serving immediately. Slice brisket against the grain and arrange on a platter. Serve with onions and pan juices.