Phase 1: Prepare and Sear the Beef (Optional but Recommended for Best Flavor)

1. Prepare the Beef: Trim any large, hard pieces of fat from your beef chuck roast (or other cut). Cut the beef against the grain into 1-inch thick strips or 1.5-inch cubes. Pat the beef pieces dry with paper towels – this helps them brown better.
2. Coat the Beef: In a medium bowl, toss the beef pieces with the 2 tablespoons of cornstarch and 1/2 teaspoon of freshly ground black pepper until lightly and evenly coated. The cornstarch helps create a nice crust when searing and gives a slight initial thickening to the sauce.
3. Sear the Beef (Optional):

   • Heat 1-2 tablespoons of vegetable oil (or a mix of vegetable and a little sesame oil for extra flavor) in a large, heavy-bottomed skillet or Dutch oven over medium-high heat until the oil is shimmering.
   • Working in batches to avoid overcrowding the pan, add the coated beef pieces in a single layer. Sear for 2-3 minutes per side, until nicely browned. Don’t worry about cooking it through at this stage; you’re just developing flavor.
   • Transfer the browned beef to the basin of your slow cooker. Repeat with the remaining beef, adding a bit more oil if needed.
   • Why sear? Searing creates a deeper, more complex meaty flavor through the Maillard reaction. If you’re short on time, you can skip this step and add the coated beef directly to the slow cooker, but the flavor won’t be quite as rich.

Phase 2: Create and Add the Sauce

1. Whisk Sauce Ingredients: In a medium mixing bowl, whisk together the 1/2 cup low-sodium soy sauce, 1/2 cup beef broth, 1/4 cup packed brown sugar, 2 tablespoons rice vinegar, 2 tablespoons toasted sesame oil, minced garlic, grated ginger, and optional red pepper flakes. Whisk until the brown sugar is mostly dissolved and all ingredients are well combined.
2. Pour Sauce Over Beef: Pour the prepared sesame sauce evenly over the beef in the slow cooker. Gently stir to ensure all the beef pieces are coated.

Phase 3: Slow Cook to Tender Perfection

1. Set Slow Cooker: Cover the slow cooker with its lid.
2. Cook: Cook on LOW for 6-8 hours or on HIGH for 3-4 hours. The beef should be very tender and easily shreddable with a fork when done. Cooking on low for a longer period generally yields the most tender results, especially for tougher cuts like chuck roast.

Phase 4: Thicken the Sauce and Finish

1. Prepare Cornstarch Slurry: About 20-30 minutes before the cooking time is complete, or once the beef is tender: In a small bowl, whisk together the 2 tablespoons of cornstarch with 3-4 tablespoons of cold water until completely smooth. This is your cornstarch slurry.
2. Thicken Sauce:

   • Remove the lid from the slow cooker. If you prefer, you can transfer the cooking liquid (leaving the beef in the slow cooker) to a small saucepan. Otherwise, you can thicken it directly in the slow cooker.
   • Pour the cornstarch slurry into the slow cooker liquid (or saucepan). Stir well to combine.
   • If thickening in the slow cooker, turn the setting to HIGH (if it wasn’t already), cover, and cook for another 15-30 minutes, or until the sauce has thickened to your desired consistency. Stir occasionally.
   • If thickening in a saucepan, bring the liquid to a simmer over medium heat, stirring constantly, until it thickens (this usually takes just a few minutes). Then pour the thickened sauce back over the beef in the slow cooker.

3. Rest (Optional): Once the sauce is thickened, you can turn off the slow cooker and let the sesame beef rest for about 10-15 minutes. This allows the flavors to meld even further.
4. Serve: Gently stir the beef in the thickened sauce. Serve hot.