Preheat the oven to 200°C (390°F). Prepare the Brussels sprouts by tossing them with 1 tbsp of olive oil, salt, and pepper. Place them on a baking sheet, cut side down, and roast for about 20-25 minutes until golden brown and tender.

In a large pot over medium-high heat, brown the stewing beef in batches if necessary to avoid overcrowding. Season the beef with salt and pepper. Once browned, remove from the pot and set aside.

In the same pot, add the chopped onions, diced carrots, and celery. Sauté the vegetables for about 5-7 minutes until they start to soften.

Stir in the tomato paste and cook for another minute until it starts to caramelize, blending it well with the vegetables.

Return the browned beef to the pot, along with any juices that have accumulated. Pour in the beef stock, and add the bay leaf and thyme. Mix well, and bring the stew to a simmer.

Once simmering, reduce the heat to low, cover the pot, and let it cook gently for about 1 hour or until the beef becomes tender.

While the stew is simmering, cook the pearl barley according to the package instructions. You may use water or a portion of the beef stock for added flavor.

After the beef is tender, stir in the cooked barley, and adjust seasoning with salt and pepper to taste. Remove the bay leaf before serving.

Serve the beef and barley stew in bowls, garnished with the roasted Brussels sprouts for a contrasting flavor and texture.