Fold heavy duty aluminum foil in half to create a 12x17-inch rectangle, with the dull side facing up and the narrow side facing you. Spray center with nonstick spray.
Place butter in a 3-inch diameter in the center of foil and sprinkle with brown sugar. Place pineapple ring inside with the maraschino cherry in the middle. Slice pound cake lengthwise in half, and cut out a circle with a round cookie cutter or a glass to match the size of the pineapple ring. Place cake round on top of pineapple.
Wrap edges around cake, and bake or grill pineapple side down for 20 minutes, caramelizing the pineapple.