For added richness, sauté the onions and mushrooms in a little olive oil before adding them to the broth.
You can substitute the vegetable broth with chicken broth for a non-vegetarian version.
Leftovers store well in an airtight container in the refrigerator for up to 3 days. Reheat gently with a splash of water to restore moisture.
Feel free to add other vegetables like diced carrots or peas for extra color and nutrition.