How to Make It
Season the brisket with salt and pepper. In a very large skillet, heat the oil until shimmering. Cook the brisket over moderately high heat, turning once, until browned on both sides, about 10 minutes total. Transfer to a slow cooker.
In a medium bowl, mix the ketchup with the brown sugar, chicken broth, onions and 1 tablespoon of the red wine vinegar. Pour the mixture over the brisket. Cover and cook on low for 8 hours, until the brisket is tender.
Transfer the brisket to a cutting board and let stand for 5 minutes. Skim the fat from the sauce. Slice the brisket across the grain 1/4 inch thick and return the meat to the sauce. Cover and cook on high for about 1 hour, until the meat is very tender. Transfer the brisket to a warm platter. Add the remaining 1 1/2 tablespoons of vinegar to the sauce and season with salt and pepper. Serve the brisket with the sauce and with buttered egg noodles.