1. Peel, halve, and core the apples.
2. Bring juice, raisins, and butter to a boil in a skillet. Lower apple halves carefully into juice mixture, reduce heat to low, and simmer gently until just soft (7-10 minutes).
3. While apples simmer, mix cornstarch with just enough cold water to make a thin paste.
4. Transfer apples to a serving dish, cut side down.
5. Stir the cornstarch mixture into the juice and simmer until thickened (2-3 minutes). Pour over apples and serve.