Finishing this oven-cooked brisket on the grill helps to caramelize the sauce, adding char and vanilla notes.
Preheat oven to 300 degrees. Heat a large pot or Dutch oven that can later be covered over medium-high heat for 2 or 3 minutes. When it is hot, add oil, swirl it around, then add beef. Sear meat for about 5 minutes on each side, seasoning with salt and pepper; when nicely browned, remove from pot. Turn off heat under pot for a minute.
Add onion to pot and cook, stirring, over medium-low heat until softened, 5 to 10 minutes (if meat is very lean you might need to add a little oil). Add all remaining ingredients, stir, and cook for about a minute. Return meat to pot, nestling it in sauce.
Cover pan, put it in oven, and cook until meat is tender, at least 2 hours and probably closer to 3. When it is done, you can refrigerate it in its liquid for 1 to 2 days before proceeding.
Light a charcoal or gas grill or heat broiler; rack should be about 4 inches away from heat source. Drain meat and sprinkle with salt and pepper. Grill or broil on both sides until brown and crisp, just a few minutes. Meanwhile, skim cooking liquid of fat, warm gently, and use as sauce.