Preheat the oven to 400°F (200°C). Prick the sweet potatoes with a fork and place them on a baking sheet. Place the apples in a baking dish large enough to hold them snugly in a single layer. Add the water and cover tightly with foil. Place the sweet potatoes and apples in the oven and roast for about an hour, until the potatoes and apples are completely tender. Check the apples after 1/2 hour and remove them if they are soft.
When the potatoes are done, cool until they are easy to handle. Cut the in half and scoop out all the flesh. Either purée the potatoes and apples together in a food processor or with a hand mixer, or mash them by hand, depending upon the texture you like.
Place in a heavy pot and stir in the butter until melted. Stir in the sour cream brown sugar and bourbon. Season with salt and pepper. Warm the mixture over low heat until heated through. The dish can be made 2 days in advance. Cover and refrigerate. Warm in a heavy pot over low heat until heated through.