In a small bowl, add the tamari or soy sauce, chicken/vegetable broth, brown sugar, and 2 tablespoons cornstarch. Whisk until combined well. Set aside.
In a medium bowl, toss the steak with 1 tablespoon of cornstarch.
Heat 2 tablespoon oil in a large cast iron skillet or large wok over medium-high heat. Add the steak and cook, stirring once until browned, about 4 minutes.
Transfer beef to a clean plate or bowl and set aside.
On same skillet or work set to medium high, add 1 tablespoon oil and the onions. Stir fry for about 45 seconds.
Add the broccoli and garlic; cook stirring occasionally until tender, about 2 minutes.
Add the beef back to the broccoli mixture. Whisk the soy sauce mixture and add to the wok/skillet.
Cook until the sauce thickens, about 1 to 2 minutes.
Serve immediately while hot with white rice. Garnish with crushed red pepper and scallions (optional)