Preheat the oven to 300°F
Trim excess fat from the brisket, leaving a thin fat cap
Pat the brisket dry with paper towels
Season all sides generously with salt, black pepper, garlic powder, and onion powder
Optional: add paprika, smoked paprika, or chili powder
Place sliced onions in the bottom of a roasting pan or Dutch oven
Set the brisket on top of the onions, fat side up
Add beef broth, water, or a mix of broth and Worcestershire sauce to the pan
Cover the pan tightly with a lid or heavy-duty foil
Bake for 1 hour per pound, or until very tender
Check for tenderness by inserting a fork; it should twist easily
If needed, continue baking until the brisket is fall-apart tender
Remove from the oven and let rest for 20 to 30 minutes
Slice against the grain or shred if it is very soft
Spoon pan juices over the brisket before serving
Optional: refrigerate overnight in the juices, then reheat for even better tenderness