1. Soak barley in cold water 2-3 hours or overnight. Rinse and drain. Place in slow cooker insert.
2. Heat oil in large saute or cast iron pan. DO NOT use non-stick surface.
3. Brown chunks of beef 6-8 minutes on each side, allowing space between each piece.
4. Place in slow cooker insert.
5. In the same pan (do not wipe it out) brown onions until golden, 12-15 minutes.
6. Add all mushrooms, stir and cook over medium heat for another 5-10 minutes.
7. Add garlic and sauté 5 minutes.
8. Place all of the above into slow cooker insert.
9. Add chopped carrots, celery, bay leaves, dill, tomato paste and broth. Season with salt and ground pepper.
10. Stir to combine well and set slow cooker to LOW and cook for 8 hours.
11. Remove bay leaves and ladle soup into bowls. Garnish with reserved chopped dill.

Tips: Barley absorbs a lot of liquid so when serving this soup, add a couple of tablespoons of water to the pot as you're re-heating it. The soup gets better with each day but it also gets thicker. DON'T worry about diluting the flavors as you add water. This broth is very rich and can handle it.