In a pot over medium heat, sauté the mushroom until browned. Set a few tablespoons of sautéed mushrooms aside for garnish.
Add in the leek and garlic. Continue to sauté until the leek is softened and reduced half in volume.
Pour in the veggie stock, cover and let it simmer until the leek is fully cooked.
With a stick blender or a standing blender, blend the soup until smooth. Add in the Yondu Vegetable Umami sauce and season to taste. Serve with toasted bread.