- 2 tablespoons olive oil or butter
- 2 cups diced onions
- 1 1/2 cups diced carrots
- 1 1/2 cups small-diced celery (with or without leaves)
- 2 tablespoons minced garlic
- 8 ounces button mushrooms, wiped clean, stemmed, and quartered (about 2 cups)
- 6 sprigs parsley
- 4 quarts beef, chicken, or vegetable stock or canned, low-sodium beef, chicken, or vegetable broth 
- 1 1/2 teaspoons salt
- 3/4 teaspoon freshly ground black pepper
- 2 cups broccoli or cauliflower florets, cut into bite-size pieces
- 1 cup diced zucchini (large dice)
- 1 cup diced yellow squash (large dice)
- 1/2 cup grated Parmigiano-Reggiano cheese (optional)
- Heat olive oil in a 6-quart or larger soup pot over high heat. Add onions, carrots, and celery and cook for 2 minutes, stirring frequently. Add garlic, mushrooms, and parsley and cook for 3 minutes. Add stock, salt, and pepper. Cover and bring to a boil. Remove cover, reduce the heat to medium-low, and simmer for 12 minutes.
- Add broccoli, zucchini, and yellow squash. Simmer 5 minutes.
- Remove parsley sprigs and serve soup hot, garnished with the grated cheese, if desired.