In the insert of a 6-quart crock pot (slow cooker), whisk together the beef stock, soy sauce, brown sugar, sesame oil, and minced garlic until well combined. This will be the flavorful base for the beef to cook in.

Place the thinly sliced sirloin steak or boneless beef chuck roast into the sauce mixture in the slow cooker. Toss the slices to ensure every piece is well coated in the sauce. Cover with the lid and cook on low heat for about 5 hours until the beef is tender and flavorful.

Once the beef is fully cooked and tender, whisk the cornstarch and water together in a small bowl to create a slurry. Pour this mixture into the slow cooker and stir well, making sure it is evenly distributed. This will help the sauce thicken up nicely as it simmers.

Scatter the frozen broccoli florets evenly over the beef and sauce in the slow cooker. Gently stir to combine everything. Cover and cook for an additional 30 minutes on low, allowing the broccoli to become tender and the sauce to thicken further. I like to give it a gentle stir halfway through to make sure the broccoli heats evenly.

Spoon the beef and broccoli mixture over warm cooked white rice, if desired, and enjoy your meal hot. For an extra special touch, I sometimes garnish with a sprinkle of sesame seeds or chopped green onions.