"The mixture sounds weird but it is actually very good. You can add potatoes and carrots if you want during the last couple of hours. This is a good recipe if you aren't going to be home all day to watch it."
Cut brisket in half across the grain and place a half into a slow cooker. Spread with half the ketchup and grape jelly; sprinkle with half the dry onion soup mix. Place remaining piece of brisket on top of the first piece and repeat spreading with remaining ketchup, grape jelly, and onion soup mix. Sprinkle black pepper into cooker.
Cover the cooker and cook on Low until meat is very tender, 8 to 10 hours.