POTATO AND BROCCOLI SOUP

2 tablespoons butter
1 onion, chopped
2 cloves garlic, minced
1 ¾ pounds broccoli, thick stems peeled and diced (about 2 cups), tops cut into small florets (about 1 quart)
1 ½ pounds boiling potatoes (about 5), peeled and cut into ½-inch cubes
3 cups canned low-sodium chicken broth or homemade stock
3 cups water
1 ¾ teaspoons salt
¼ teaspoon fresh-ground black pepper
½ cup grated parmesan

1. In a large pot, melt the butter over moderately low heat. Add the onion; cook, stirring occasionally, until translucent, about 5 minutes.
2. Add the garlic, broccoli stems, potatoes, broth, water, salt, and pepper. Bring to a boil. Reduce the heat and simmer until the vegetables are almost tender, about 10 minutes
3. In a food processor or blender, pulse the soup to a coarse puree. Return the soup to the pot and bring to a simmer. Add the broccoli florets and simmer until they are tender, about 5 minutes. Stir ¼ cup of the grated parmesan into the soup, and serve the soup topped with the remaining cheese.