Core apple; remove peel from top 1/2 inch. In a bowl, mix raisins, sugar and butter. Pack mixture into core of apple.
Place apple right side up in a microwave-safe bowl. Pour in 1/2 cup water. Sprinkle cinnamon over top of apple. Cover bowl with microwave-safe plastic wrap, leaving a small space for steam to escape, and cook in microwave on full power for 5 minutes, or until apple is fragrant and soft, checking every 2 minutes (microwave cooking times vary).
Remove apple from bowl, place on a clean small plate and pour 1 tsp. of cooking liquid over apple. Serve warm.