Preheat the oven to 350°.
Cut the sweet potatoes into thick slices.
Steam the chunks of carrots in the microwave for 6 minutes, or until they are semi-hard when you prick with a fork.
In a 2-quart casserole dish, mix the sweet potato slices, carrots, pineapple, and prunes together. Set aside.
In a small bowl, use a wire whisk to whisk together the cornstarch, pineapple juice, brown sugar, and salt to make a syrup.
Use a rubber spatula to mix in the syrup with the sweet potatoes, carrots, pineapple chunks, and prunes, covering everything with the syrup.
Cover the casserole dish with aluminum foil and seal it around the edges. Bake it at 350° for 1 hour.
Lift the aluminum foil. Stir it. Seal the aluminum foil back on top and bake it for another ½ hour.