01 - In a medium bowl, whisk together soy sauce, brown sugar, beef broth, sesame oil, rice vinegar, garlic, ginger, and gochujang until well combined and sugar has dissolved.
02 - Place beef cubes and sliced onion in the crock pot. Pour sauce mixture over beef and onions, tossing gently to coat evenly.
03 - Cover and cook on low for 6-7 hours or on high for 3-4 hours, until beef is fork-tender and easily shredded with a fork.
04 - Remove 1/4 cup cooking liquid and whisk with cornstarch until smooth. Stir cornstarch slurry back into crock pot, cover, and cook on high for 20-30 minutes until sauce thickens.
05 - Serve Korean beef over steamed rice, noodles, or in lettuce wraps. Garnish with green onions and toasted sesame seeds.