Coat the beef: Toss the sliced beef chuck with 1/4 cup of the cornstarch until evenly coated. This light coating helps the meat brown and later helps thicken the sauce.

Sear in batches: Heat the oil in a large skillet over medium-high heat. Sear the beef in batches for about 3 minutes per side, until the edges turn deep golden, then transfer to the slow cooker.

Whisk the sauce: In a bowl, whisk together the soy sauce, brown sugar, garlic, ginger and beef broth until the sugar fully dissolves.

Pour over beef: Pour the sauce over the seared beef in the slow cooker, stirring once so every piece is coated.

Cook low and slow: Cover and cook on low for 6 hours or on high for 3 hours, until the beef shreds easily with a fork.

Mix the slurry: In a small bowl, whisk the remaining cornstarch with the water until smooth, with no lumps remaining.

Thicken the sauce: Stir the slurry into the slow cooker and cook uncovered on high for 10-15 minutes, stirring occasionally, until the sauce turns glossy and coats the back of a spoon.

Garnish and serve: Scatter the green onions and sesame seeds over the top. Spoon the beef and sauce over cooked white rice and serve hot.