In a small bowl, whisk together broth, cornstarch, curry powder, garlic, salt and pepper until cornstarch has dissolved; set aside.
In a large skillet, heat half of the oil over medium-high heat. Add half of the beef slices, salting and peppering to taste; cook, stirring occasionally, until browned, about 2 minutes; remove from skillet keep warm. Repeat this process with remaining beef slices.
In the same skillet, heat remaining oil; add onions and cook until softened and slightly browned, about 4 minutes. Return beef slices and their juices to the skillet along with the broth mixture. Cook until sauce has slightly thickened.