Heat the vegetable broth in a saucepan and keep it warm on low heat.

In a large pan, heat olive oil over medium heat. Add the chopped onion and sauté until translucent, about 3-4 minutes.

Add the minced garlic and sliced mushrooms to the pan. Cook until the mushrooms are tender and browned, about 5-6 minutes.

Stir in the pearl barley and toast for 1-2 minutes until lightly fragrant. Pour in the white wine and cook until it has mostly evaporated.

Begin adding the warm broth, one ladle at a time, stirring frequently. Allow each addition to be absorbed before adding the next.

Continue this process for about 30-35 minutes until the barley is tender and the mixture is creamy.

Stir in the butter, grated Parmesan cheese, and thyme. Season with salt and black pepper to taste.

Garnish with fresh parsley and serve hot.