Brown the Beef: In a large pot or Dutch oven, heat the olive oil over medium-high heat. Add the beef stew meat and cook until browned on all sides, about 5-7 minutes. Remove the beef from the pot and set it aside.

Sauté the Vegetables: In the same pot, add the diced onion, sliced carrots, and chopped celery. Cook for 5 minutes or until the vegetables start to soften, stirring occasionally. Add the minced garlic and cook for another 1-2 minutes, until fragrant.

Add the Broth and Seasonings: Pour in the beef broth and diced tomatoes (including their juice). Return the browned beef to the pot. Add the pearl barley, bay leaf, and fresh thyme. Stir well to combine.

Season and Simmer: Season the soup with salt and black pepper to taste. Bring the mixture to a gentle boil, then reduce the heat to low. Cover the pot and let the soup simmer for 1-1.5 hours, or until the beef and barley are tender, stirring occasionally.

Adjust Seasonings and Garnish: Once the beef and barley are tender, taste the soup and adjust the seasonings if necessary. Remove the bay leaf and discard. If desired, garnish each bowl with fresh parsley.

Serve: Ladle the soup into bowls and serve warm, paired with crusty bread for a hearty and satisfying meal.