Begin by evenly chopping carrots, celery, and onion into bite-sized pieces, and mincing the garlic cloves to release their aroma.
In a skillet over medium-high heat, fry the beef chunks until browned on all sides, hearing a gentle sizzle and watching them develop a rich, golden crust.
Transfer the browned beef to the slow cooker, then add the chopped vegetables, minced garlic, and barley directly on top.
Pour in the beef broth, stirring in tomato paste, thyme, and dropping in a bay leaf, then season with salt and pepper according to your taste.
Cover the slow cooker with its lid, set to low, and cook for about 4 hours, until the beef is tender and the barley has expanded into a hearty, chewy texture.
Once cooking is complete, remove the bay leaf and give the soup a gentle stir, allowing the ingredients to meld and thicken the broth slightly.
Taste the soup and adjust seasoning with more salt and pepper if needed, ensuring a balanced, savory flavor.
Serve the soup hot, garnished with fresh herbs or a squeeze of lemon if desired, enjoying its thick, chunky texture and rich aroma.