Preheat the oven to 300°F
Trim excess fat from the brisket, leaving about 1/4 inch fat cap
Pat the brisket dry with paper towels
Season generously with salt, black pepper, garlic powder, and onion powder
Optional: rub with paprika, chili powder, or brown sugar
Place the brisket fat-side up in a roasting pan or Dutch oven
Add sliced onions, garlic, and a small amount of beef broth if desired
Cover tightly with a lid or heavy-duty foil
Bake for about 1 hour per pound
Check for tenderness after the estimated cooking time
Continue cooking until the brisket is fork-tender
Remove from the oven and let rest for 20 to 30 minutes
Slice brisket against the grain
Serve with pan juices or gravy