Preheat your oven to 325°F (165°C).
Pat the brisket dry with paper towels. Place it fat-side up in a large roasting pan or Dutch oven.
Sprinkle the dry French onion soup mix evenly over the brisket. Pour the condensed French onion soup over the top, spreading it around so the meat is well coated.
Cover the pan tightly with foil or a lid. Bake for 3 to 3½ hours, or until the brisket is very tender and easily pierced with a fork. Larger or thicker briskets may need additional cooking time.
Remove the brisket from the oven and let it rest, covered, for 15–20 minutes. This allows the juices to settle back into the meat.
Slice the brisket against the grain and spoon the rich French onion gravy over the top.
