Cannellini Soup with Parmesan

3 tablespoons extra-virgin olive oil plus additional oil for garnish
1 large onion, finely chopped (about 2 cups)
1 large carrot, finely chopped (about 1 cup)
1 large celery stalk, finely chopped (about 2/3 cup)
3 15-ounce cans cannellini (white kidney beans), drained
6 cups low-salt chicken broth or vegetable broth
2 teaspoons minced fresh sage
2 2x2-inch Parmesan cheese rinds
3 ounces thinly sliced prosciutto, chopped (optional)

Heat 3 tablespoons oil in heavy large pot over medium heat. Add onion, carrot, and celery and sauté until vegetables are soft, about 10 minutes. Add beans, broth, sage, Parmesan rinds, and prosciutto; simmer over medium-low heat, stirring occasionally, until flavors blend and soup thickens slightly, about 30 to 40 minutes. Using tongs, remove cheese rinds.  Season with salt and pepper.

Makes 4 to 6 servings.

From Epicurious/ Bon Appétit