In a saucepan combine the potatoes, peeled and cut into 1/2-inch pieces, the cauliflower leaves, the white part of scallion, the caraway seeds, and 3 1/2 cups water, simmer the mixture for 15 minutes, or until the potatoes are very tender, and in a blender or food processor purée the mixture coarse. In the pan combine the purée and the flowerets, simmer the soup for 5 minutes, or until the flowerets are tender, and stir in the scallion greens and salt and pepper to taste. Serve the soup sprinkled with the Parmesan.
