Slow-cooker beef barley soup is made with tender beef stew meat, chewy barley, fresh celery, chopped onions, medium carrots, and other nutritious veggies with seasoning and fresh herbs.
In a large skillet with some cooking oil, brown the mushrooms until they become golden brown. Set aside.
In the same skillet, add more oil and sear the beef chunks over medium-high heat. About 2 minutes per side.
Transfer all the ingredients to a crock pot (I used a 4.5-quart slow cooker), and season with salt and black pepper.
Cook on LOW for 6 hours or HIGH for 4 hours. Discard the bay leaves and serve right away with fresh parsley and sour cream.