Prepare the Beef: Pat the sliced beef dry with paper towels. In a medium bowl, toss the beef slices with 2 tablespoons of the cornflour until they are lightly and evenly coated.

Sear the Beef (Optional but Recommended): Heat the vegetable oil in a large frying pan over medium-high heat. Working in batches to avoid overcrowding the pan, add the beef and sear for 1-2 minutes per side, just until browned. The beef doesn't need to be cooked through. Transfer the seared beef to the bowl of your slow cooker. I find that this step is crucial for developing a deep, beefy flavour; you can learn more about the science behind it from experts like Serious Eats.

Mix the Sauce: In the same bowl you used for the beef (no need to wash it), whisk together the low-sodium soy sauce, beef broth, brown sugar, sesame oil, minced garlic, grated ginger, and black pepper until the sugar has dissolved.

Combine and Cook: Pour the sauce mixture over the seared beef in the crockpot. Give everything a gentle stir to combine. Secure the lid and cook on LOW for 4-6 hours or on HIGH for 2-3 hours. I much prefer the texture of the beef when cooked on low.

Prepare the Thickener: About 30 minutes before the cooking time is up, prepare the cornflour slurry. In a small bowl, whisk the remaining 1 tablespoon of cornflour with 2 tablespoons of cold water until smooth.

Add Broccoli and Thicken: Stir the cornflour slurry into the slow cooker. Add the broccoli florets and gently push them down into the sauce.

Final Cook: Replace the lid and continue to cook on HIGH for another 20-30 minutes, or until the broccoli is tender-crisp and the sauce has thickened to a glossy consistency.

Serve: Give everything a final stir. Serve the beef and broccoli hot over steamed rice or noodles, garnished with a sprinkle of toasted sesame seeds and sliced spring onions.