Brown beef in oil over medium-high heat in a large pot, 5–7 minutes. Don’t crowd the pan; do batches if needed.
Add onion, carrots, and celery; cook 4 minutes until soft. Stir in garlic and tomato paste for 1 minute.
Pour in beef broth, water, thyme, bay leaf, and barley. Scrape brown bits from the bottom.
Bring to a simmer, cover, and cook low 45–60 minutes until beef and barley are tender. Stir occasionally.
Cool completely, portion into freezer bags, label, and freeze flat. To reheat, thaw overnight and simmer 20–30 minutes; or from frozen, simmer 45–60 minutes.