Season the beef with 1 teaspoon of Kosher salt and ¼ teaspoon of freshly ground black pepper.
Over medium high heat, heat a few drizzles of olive oil on a large 6 or 8 quart Dutch oven pot. Sear the beef on all sides until nicely browned. Do this in batches to not overcrowd the pan (this will prevent steaming). Tip: If you notice that it begins to steam up, remove the excess liquid and continue browning.
Transfer the browned meat to a plate and set aside. It will not be fully cooked at this point. Leave the brown bits, don’t wipe the pot clean.
To the pot, add a few more drizzles of olive oil, and over medium high heat, cook the onions, celery and carrots for about 10 minutes until softened. The moisture from the veggies will release the brown bits (left from searing the meat) and add a lot of flavor.
Add the minced garlic, mushrooms, and fresh thyme leaves. Cook for another 2 minutes until fragrant, stirring.
Stir in the canned diced tomatoes and the Worcestershire sauce. Return the cooked meat to the pot. Add 5 cups of beef broth and 1 cup of water, and stir until combined. Season with salt and pepper to taste. Bring to a boil, and then reduce heat to a low simmer. Simmer for 30 minutes, with the lid covered.
After that, stir in the pearl barley. Bring to a boil and reduce heat to a simmer. Simmer for another 40-45 minutes with the lid covered, or until the barley is fully cooked and tender. Stir occasionally. If needed, add more broth and/or water (check a few times if more liquid is needed because barley tends to absorb liquid). Tip: for more tender barley, cook for an additional 10 minutes or so.
Adjust seasonings with salt and pepper if needed. Serve with some fresh parsley or thyme as garnish. Enjoy!