Remove any excess fat from the beef and cut into small ½-inch cubes. Season with 1 teaspoon Kosher salt and ½ teaspoon of freshly ground black pepper.
Heat a few drizzles of olive oil in a large 6-quart Dutch oven over medium-high heat. Sear the beef until nicely browned. Do this in batches to not overcrowd the pan to prevent steaming. Letting the beef sear undisturbed for a few minutes will get you a better sear. Tip: If you notice extra liquid, absorb it with paper towel.
Transfer the browned meat to a plate and set aside. It will not be fully cooked at this point. Don’t wipe the pot clean - those brown bits are packed with flavor.
To the same pot, add a few more drizzles of olive oil. Sauté the onions, celery and carrots for about 8 minutes until softened. The moisture released from the veggies should help deglaze the brown bits. If not, add a splash of broth to deglaze.
Then, add the minced garlic, thyme, and mushrooms. Cook for another 3 minutes until fragrant, stirring.
Stir in the canned diced tomatoes and the Worcestershire sauce. Return the cooked meat to the pot, and add the beef broth and the water. Season with salt and pepper to taste. Bring to a boil and then reduce heat to a low simmer. Simmer for 35 minutes, covered.
Next, stir in the pearl barley. Bring back to a simmer and cook for another 40 minutes (covered) until the barley is tender and the soup is slightly thickened, stirring occasionally. Adjust the amount of broth to taste, as well as more salt and pepper if needed.
Serve warm with fresh parsley as garnish. Enjoy with some warm bread.