Slow-Cooker Beef and Barley

INGREDIENTS

• Kosher salt and freshly ground pepper
• 1 tablespoon soy sauce
• 1/2 pound cremini mushrooms, quartered
• Horseradish, for serving (optional)
• 4 cups low-sodium beef broth
• 6 medium carrots, quartered
• 2 medium leeks, sliced (white and light green parts only)
• 1 sprig thyme
• 4 stalks celery, quartered
• 1 1/4 pounds boneless beef chuck (in one piece)
• 1 cup pearl barley