To remove panna cotta from ramekins, carefully run offset spatula or thin knife around edge of each panna cotta. Dip bottom of each ramekin into bowl of very hot water 5 seconds. Immediately place serving plate upside down over each ramekin; turn plate and ramekin over, and remove ramekin. Spoon or pipe about 2 tablespoons marshmallow frosting on top of each panna cotta. Top each with 2 teaspoons crushed cereal.