Heat the olive oil in a large pot over medium heat. Add the onion, carrot, celery, 1/2 teaspoon salt, and 1/4 teaspoon pepper and cook, stirring occasionally, until the vegetables are soft and the onions are translucent, about 8 minutes.
Add the water and/or broth, the Parmesan rind and the corn cob (if using). Bring to a boil, then reduce heat and simmer uncovered until the carrots are just tender, about 10 minutes.
Add the corn kernels, zucchini and green beans and cook until all the vegetables are tender and the flavors have developed, about 10 minutes more. Discard the cheese rind and corn cob. Add the rice and cook for another 2 minutes, then stir in the greens. Once they begin to wilt, turn off the heat. Check for seasoning and, if necessary, add more salt and pepper. Ladle the soup into bowls and top with Parmesan and/or a squeeze of lemon juice.
This adaptable soup template will see you through almost any odds and ends you may have in your kitchen. Basic Kitchen Sink Soup Template: 2 cups aromatic base (onion, carrot and celery) 5 cups liquid, such as water, stock, or reserved cooking liquid 3 cups mixed vegetables, cut into bite-sized pieces 1 cup cooked starch or grain, such as rice, pasta, quinoa or barley 2 cups quick-cooking greens, such as lettuce, baby spinach or watercress 2 tablespoons chopped fresh soft herbs, such as parsley, cilantro or dill
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