In a medium soup pot prepare leeks and garlic by heating 2 tablespoons of oil together with the cooking spray over medium heat for a few seconds. Add the leeks and onions; stir and lower heat.
Cook until the leeks and onions start to brown. Stir occasionally. Add 3 cloves garlic and water, the mixture will start to brown. Cook another few minutes, scraping the bottom of the pan so that nothing sticks.
Add mushrooms, seasoning and liquid. Bring to a boil then simmer on medium heat for 25-30 minutes.
Let soup cool. Fish out a few mushrooms for garnish, then sprinkle with soy or regular flour and blend with an immersion blender or process in food processor with knife blade.
Boil soup on high heat for 1 minute. Turn off heat and add soy milk (and barley, if desired), then stir. Make sure not to boil after adding the soy milk, so that it does not curdle. Return unblended mushrooms for garnish.