In small bowl, whisk together cornstarch and 2 tablespoons cold water. In medium bowl, whisk garlic, 1 cup beef broth, soy sauce, ginger, sesame oil, sriracha and black pepper until smooth. 

Heat very large skillet or wok over medium heat. Add beef and cook 6 to 8 minutes or until meat is cooked through, breaking up meat with side of spoon as it cooks. Use slotted spoon to transfer beef to plate.

Add remaining 1/4 cup beef broth to skillet and use a wooden spoon to scrape the crusty bits of meat off the bottom and side of skillet (but you can leave the crusty bits in the skillet after scraping them).

Increase heat to medium-high and add carrots, onion, bell pepper and broccoli to skillet. Cook 8 to 10 minutes or until vegetables are tender-crisp, stirring occasionally. Add beef and any juices from the plate back to skillet.

Reduce heat to low and add the soy sauce mixture; heat to simmering. Give the cornstarch mixture another whisk and slowly pour it into the skillet while stirring the beef mixture. Cook 2 to 3 minutes or until sauce thickens and glazes meat and vegetables.

Serve over rice, garnished with sesame seeds, if desired.