Summarize:

Remove the cinnamon stick and spoon the arroz con leche into serving bowls. Sprinkle a dusting of cinnamon over the tops and serve them warm. If you prefer to serve cold arroz con leche, cover it with plastic wrap and press down on the surface to prevent a skin from forming. Refrigerate the arroz con leche for up to 5 days.
Sprinkle a little cinnamon over the arroz con leche before serving.