Rinse the uncooked white rice under cold water until the water runs mostly clear, then drain well.

In a medium saucepan, combine the rinsed rice and 2 cups of water. Bring to a gentle boil over medium-high heat.

Once boiling, reduce the heat to low, cover with a tight-fitting lid, and simmer for about 15 minutes, or until the water is absorbed and the rice is tender.

Remove the rice from the heat and let it sit, covered, for 5 minutes to steam, then fluff gently with a fork and keep warm.

Place the thinly sliced beef sirloin in a bowl. Add 1 tablespoon of cornstarch, the salt, and the black pepper. Toss until the beef is evenly coated and set aside.

In a small bowl or measuring cup, combine the soy sauce, beef broth, brown sugar, and rice vinegar. Stir until the brown sugar is mostly dissolved.

In a separate small bowl, stir together 1 tablespoon of cornstarch and 2 tablespoons of water until smooth to create a cornstarch slurry, then set aside.

Heat 1 tablespoon of vegetable oil in a large skillet or wok over medium-high heat.

Add the broccoli florets to the hot pan and stir-fry for 3 to 4 minutes, or until they are bright green and crisp-tender. Transfer the broccoli to a plate and set aside.

In the same skillet or wok, add the remaining 1 tablespoon of vegetable oil and heat over medium-high heat.

Add the coated beef slices in an even layer. Cook for 2 to 3 minutes without moving too much to allow them to brown, then stir-fry for another 2 to 3 minutes until the beef is mostly cooked through.

Add the minced garlic and grated ginger to the beef. Stir-fry for about 30 seconds, just until fragrant, being careful not to burn the garlic.

Give the soy sauce mixture a quick stir and pour it into the pan with the beef, stirring to coat the slices evenly.

Bring the sauce to a gentle simmer, then stir the cornstarch slurry once more and drizzle it into the pan while stirring constantly.

Continue to cook for 1 to 2 minutes, stirring, until the sauce thickens and becomes glossy and the beef is cooked through.

Return the cooked broccoli florets to the pan and toss everything together until the broccoli is coated in the sauce and heated through.

Taste and adjust seasoning if desired, then remove the skillet from the heat.

To serve, spoon a portion of the warm cooked rice into each bowl or plate and top with the beef and broccoli mixture along with some of the savory sauce.