Place 1 teaspoon butter in 1 side of sandwich iron. Hold over fire to melt; remove from fire. Carefully sprinkle 1 tablespoon brown sugar over melted butter. Top with pineapple ring; add cherry to center of pineapple. Top with cake (flat side up); close iron. , Cook pineapple side down over a hot campfire until brown sugar is melted and cake is heated through, 5-8 minutes. Invert iron to open, and serve cake on an individual plate.