01 - Pat the beef chuck roast thoroughly dry with paper towels. Season both sides generously with salt and freshly ground black pepper.
02 - Whisk together soy sauce, beef broth, brown sugar, sesame oil, minced garlic, grated ginger, rice vinegar, and gochujang in a medium bowl until the sugar dissolves completely.
03 - Arrange sliced onions, carrots, and baby potatoes in an even layer at the bottom of a 6-quart or larger slow cooker.
04 - Place the seasoned beef roast on top of the vegetable bed. Pour the prepared marinade over the beef and vegetables, ensuring all surfaces are thoroughly coated.
05 - Cover the slow cooker with the lid. Cook on LOW setting for 8 hours until the beef pulls apart easily with a fork.
06 - Carefully remove the beef and vegetables from the slow cooker using tongs or a slotted spoon. Arrange on a large serving platter and cover loosely with foil to keep warm.
07 - Pour the cooking liquid from the slow cooker into a medium saucepan. Bring to a gentle simmer over medium heat, skimming any excess fat from the surface.
08 - Combine cornstarch and water in a small bowl, whisking until smooth. Gradually whisk the slurry into the simmering liquid. Continue cooking for 2 to 3 minutes, stirring constantly, until the gravy thickens and coats the back of a spoon.
09 - Using two forks, shred the beef into bite-sized pieces against the grain. Serve the shredded beef alongside vegetables, ladled generously with the thickened soy garlic gravy.
10 - Sprinkle with sliced scallions and toasted sesame seeds immediately before serving.