Cook sweet potatoes in boiling salted water to cover until almost tender; drain.
Peel potatoes and cut into crosswise slices, 1/4 inch thick.
Toss apples with lemon juice.
Butter a 1 1/2 quart baking dish.
Arrange half of the sweet potatoes in bottom and cover with half of the apple slices.
Sprinkle with half of brown sugar.
Dot with 2 tablespoons of the butter.
Pour apple juice over all.
Bake at 350Â°F about 45 minutes.