Preheat the oven to 375 degrees . Roll out the dough and press into a 4-by-14-inch rectangular or 9-inch round tart pan with a removable bottom; trim the top edge. Set the pan on a baking sheet. Prick the dough several times with a fork and bake until lightly golden, 15 minutes. (Prick the tart shell if the dough puffs up during baking.)
Meanwhile, in a medium saucepan, cover the sweet potato slices with water and bring to a boil. Cook until tender, about 15 minutes. Strain and mash until smooth. Transfer 1 cup to a bowl.
In a small, nonstick skillet, cook the banana slices with the dark brown sugar over medium heat, turning once, until caramelized, about 5 minutes. Mash the banana into the sweet potato, then stir in the eggs, cream, raw sugar, light brown sugar, pumpkin pie spice and salt.
Pour the mixture into the prebaked tart shell and bake until slightly puffed and set, about 35 minutes. Let cool on a rack at least 3 hours, or refrigerate overnight.
