Heat the milk on medium heat and mix with the cinnamon and lemon peels until boiling. Add rice and lower heat. Let simmer for 45/50 minutes, stirring ever five minutes at first, then constantly to prevent sticking. Add the sugar toward the end along with the butter for more creaminess, if desired.
It should be more liquid at this stage, as it will thicken as it cools. As it cools remove the cinnamon sticks and lemon peels and pour into individual bowls or into a larger bowl. Once cool, sprinkle with sugar and carmelize with a hot iron creating a thin crust. Or, sprinkle with powdered cinnamon. You can also decorate it with the cinnamon sticks and lemon peels. Serve room temperature or cold.
Will last two or three days in the refigerator covered with wax paper. Over time it will continue to thicken.
Luis Veira, Árbore da Veira Restaurant (Coruña Cociña)