Pat the beef cubes dry with a paper towel and season generously with salt and black pepper.
Heat 1 tablespoon of olive oil in a Dutch oven over medium-high heat. Sear the beef cubes in batches until nicely browned on all sides (about 4–5 minutes per batch). Transfer beef to a clean plate.
Lower heat to medium and add the remaining oil. Sauté the onion, carrots, celery, and mushrooms for 5–6 minutes until softened. Stir in the minced garlic and cook for 1 minute.
Pour in 1/2 cup of the beef broth, scraping up all the browned bits from the bottom of the pot with a wooden spoon.
Return the beef and any resting juices to the pot. Pour in the remaining beef broth, pearl barley, Worcestershire sauce, dried thyme, and bay leaf.
Bring to a boil, then reduce heat to low, cover tightly with a lid, and let simmer for 45–50 minutes, stirring occasionally, until the beef and pearl barley are wonderfully tender.
Remove and discard the bay leaf. Season with additional salt and pepper to taste and serve hot.