Add milk, rice, cinnamon stick, lemon rind, and orange zest to a medium pot. Split the vanilla pod in half lengthwise with a tiny knife, scoop the seeds into the pan, and remove the pod (add vanilla essence later).
1
To avoid sticking, stir the milk and rice for the first 3 minutes while you simmer the mixture over low to medium heat.
2
Continue cooking rice, whisking frequently every six minutes, until soft and thickened. This should take 35-40 minutes. Taste a grain to verify rice cooking. It must be soft. Milk should be creamy like heavy cream.
3
Dilute cornstarch with ¼ cup water in a small dish. Whisk into the rice mixture over low heat until the pudding thickens but is still pourable. Watch out—this will happen rapidly. Stop cooking.
4
Discard the lemon rind and cinnamon stick. Mix in sugar and lemon zest (if using). Taste and add sugar if needed.
5
Sprinkle ground cinnamon over 5 serving bowls of pudding. It may be eaten warm, room temperature, or cold.
6