Heat 1 tablespoon of olive oil in a large Dutch oven or heavy soup pot over medium-high heat. Add the cubed beef, season with salt and pepper, and sear until beautifully browned on all sides (about 5-7 minutes). Remove the beef to a plate and set aside.
Add the remaining 1 tablespoon of olive oil to the same pot. Add the onion, carrots, and celery. Sauté for 5-6 minutes, scraping up the browned beef bits from the bottom of the pot, until the vegetables are softened.
Stir in the minced garlic and dried thyme, cooking for 1 more minute until fragrant.
Return the browned beef (and any accumulated juices) to the pot. Pour in the beef broth, undrained diced tomatoes, and the rinsed pearl barley. Drop in the bay leaf.
Bring the soup to a boil. Once boiling, immediately reduce the heat to low, cover the pot tightly, and let it simmer gently for 1 hour to 1 hour and 15 minutes.
Check for doneness. The beef should be incredibly tender and the barley should be soft and plump.
Discard the bay leaf. Taste the broth and adjust the seasoning with more salt and pepper if needed. Serve hot with crusty bread!