Preheat the oven to 375 degrees. Wash the potatoes and pierce them with a fork. Bake for about 1 hour or until soft when pierced with the point of a knife. When cool enough to handle, peel the potatoes and place in the bowl of a food processor. Add the butter, sour cream, and maple syrup and pulse until the potatoes are smooth. Season to taste with salt and pepper. Transfer to a casserole, cover, and keep warm until ready to serve.