Position a rack in the center of the oven and preheat the oven to 400 degrees . Grease a 9-by-13-inch baking dish. In a 1-qt., heavy-bottomed saucepan, cook the sugar, without stirring, over medium heat until it begins to melt. Continue to cook, stirring occasionally with a wooden spoon, until the sugar turns a deep golden caramel color. Remove the melted sugar from the heat and carefully stir in the apple juice, 2 tbsp. butter, 1/2 tsp. salt and 1/4 tsp. pepper. (Heads up: The caramel will bubble up, harden and steam vigorously.) Return to medium-low heat and cook, stirring, until the caramel is dissolved. Let the caramel sauce cool for about 10 minutes.
In a large bowl, toss the caramel sauce with the sweet potato and apple cubes; transfer to the prepared baking dish. Cover the baking dish with foil and bake, stirring once, until the apples and sweet potatoes are tender, about 35 minutes.
Meanwhile, in a large skillet, melt the remaining 3 tbsp. butter over medium heat. Add the bread cubes and 1/4 tsp. each salt and pepper; toss to coat evenly. Cook the bread cubes, stirring occasionally, until they are lightly toasted.
Uncover the casserole and sprinkle the croutons on top. Bake until deep golden, about 10 minutes longer. Top with the parsley.