For a richer flavor, consider using a combination of vegetable broth and mushroom broth. Feel free to add other vegetables to the soup, such as zucchini, corn, or peas. If you prefer a thicker soup, you can add a cornstarch slurry (1 tablespoon cornstarch mixed with 2 tablespoons cold water) during the last few minutes of cooking. Garnish with extra fresh parsley before serving for added freshness.