In a large soup pot or stockpot, sauté the mushrooms, onion and garlic for 3 – 5 minutes, until the onions become soft. Reduce heat to medium-low and add the vegetable broth. Cover and allow to simmer for at least 4 – 5 minutes. Add the flour and soy milk or coconut milk, stirring well to combine. Allow to simmer for another 20 – 30 minutes, or until the soup has thickened. Season generously with salt and pepper before serving.