Begin by preparing the sauce for your Chinese Beef and Broccoli. In a medium bowl, mix together the cornstarch, water, sugar, dark soy sauce, light soy sauce, Chinese cooking wine, Chinese five spice powder, sesame oil (if using), and black pepper. Stir the ingredients well until the cornstarch is fully dissolved and the mixture is smooth.

Next, slice your beef into thin strips, about 0.5 cm thick, cutting against the grain. Combine the beef with two tablespoons of the prepared sauce in a bowl and mix until well-coated. Set the beef aside to marinate for about 10 minutes.

Heat a large skillet or wok over high heat and add a splash of oil. Sear the marinated beef for approximately 1 minute, flipping occasionally, until cooked through.

Quickly toss in the finely chopped garlic and ginger to the skillet. Stir-fry for about 30 seconds until fragrant, taking care not to let them burn.

Pour the remaining sauce and an additional splash of water into the skillet with the beef. Stir everything briskly and bring it to a simmer over medium-high heat.

Add the cooked broccoli florets to the skillet and stir to coat them in the thickened sauce. Allow to simmer for about 1 minute.

Remove the skillet from heat and serve your Chinese Beef and Broccoli immediately over a bed of rice. Sprinkle sesame seeds on top if desired.