Scrub carrots, cut half lengthwise and simmer in slightly salted water for 15 minutes. (Unsalted chicken broth makes a nice substitute for the water) Add the diced potato and simmer for 15 more minutes or until vegetables are tender. Preheat oven to 350F Drain the vegetables, reserving the cooking liquid for the next step. Puree the carrots and potatoes in a blender, adding cooking liquid as needed to keep the mixture from getting pasty. Blend in the butter and Parmesan cheese and season with salt. Pour into an ovenproof dish Bake uncovered for 10 minutes. Garnish with chopped parsley just before serving.