Heat olive oil in a large Dutch oven over medium-high heat until shimmering. Working in two batches to avoid overcrowding, sear the beef chuck cubes for 3-4 minutes per side until deeply browned, then transfer to a plate.

In the same pot, add diced onion, sliced carrots, and chopped celery, cooking for 5-6 minutes while stirring occasionally until vegetables soften and release their aromatics. This mirepoix base builds foundational flavor for your best beef barley soup.

Stir in minced garlic and tomato paste, cooking 2 minutes until the paste caramelizes slightly and becomes deeply fragrant. The raw garlic converts to sweet, mellow notes during this brief sauté.

Add sliced mushrooms and cook 4-5 minutes until they release their liquid and begin to brown slightly, then return the seared beef to the pot. Pour in beef broth, diced tomatoes, pearl barley, bay leaves, thyme, rosemary, salt, and pepper, stirring thoroughly.

Bring the soup to a simmer, then reduce heat to maintain a gentle bubble for 40-45 minutes until the beef becomes fork-tender and barley softens completely. Skim any foam that rises during the first 10 minutes.

Taste and adjust seasoning as needed, removing bay leaves before serving. The broth should coat the back of a spoon from the released barley starches.