Mushroom Tortellini and Escarole Soup

Description
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Ingredients

 * 2 tsp. olive oil
 * 1 small onion, finely chopped ( 1/2 cup)
 * 3 shiitake mushrooms, sliced ( 1/2 cup)
 * 7 cups vegetable broth
 * 5 cups chopped escarole
 * Grated Parmesan cheese (optional)

Directions
In large pot, heat oil over medium heat. Add onion and mushrooms and cook, stirring often, until softened, about 3 minutes. Add vegetable broth and heat through. Add escarole and cook 2 minutes. Add cooked tortellini and heat through. Serve with Parmesan cheese if desired.