Trim excess fat from the brisket, leaving about 1/4 inch fat cap
Pat the brisket dry
Season generously with salt, black pepper, and any desired dry rub
Let the brisket sit at room temperature for 30 to 60 minutes
Preheat the oven to 275°F
Place the brisket in a roasting pan or Dutch oven, fat side up
Add onions, garlic, and a small amount of beef broth or water if desired
Cover tightly with a lid or foil
Cook until tender, about 1 to 1.5 hours per pound
Check for doneness when the internal temperature reaches 195°F to 205°F
Remove the brisket from the oven
Rest the brisket for 30 to 60 minutes
Slice the brisket against the grain
Serve with the pan juices or sauce