In the insert of the crockpot, whisk together beef broth, soy sauce, brown sugar, sesame oil, and garlic.
Place slices of beef in the liquid and toss to coat. Cover with lid and cook on low heat for 4 hours.
After 4 hours whisk together cornstarch and water in small bowl. Pour into crock pot and stir to mix well. Add the broccoli and gently stir to combine. Cover with lid and cook 30 minutes on high to cook broccoli and thicken sauce.