Heat the oven to 350°F and season the beef with 1/2 teaspoon salt and the pepper.
Heat 1 tablespoon oil in a Dutch oven over medium-high heat and brown the beef in two batches for 3 to 4 minutes per batch, then transfer it to a plate.
Add the remaining oil, mushrooms, onion and carrots and cook for 7 minutes, until the mushrooms lose their raw look and begin to brown.
Stir in the tomato paste and rosemary and cook for 1 minute, scraping the browned bits from the pot.
Add the barley, broth, remaining salt and beef with its juices and bring the mixture to a simmer.
Cover the pot and bake for 75 to 90 minutes, until the beef is fork-tender and the barley is chewy but no longer hard.
Rest uncovered for 10 minutes, adding 1/4 cup hot water only if the barley absorbed every drop of broth.