Pour the milk, lemon peel, orange peel, and cinnamon stick into a saucepan.

When it comes to a boil, remove from heat and cover. Let it sit for 30 minutes.

In a bowl, whisk together the egg yolks and sugar, then add the cornstarch and mix until combined.

Strain the milk and gradually add it to the egg mixture, stirring to combine.

Return the mixture to the heat and cook, stirring constantly.

When it thickens, refrigerate overnight.

Five minutes before serving, divide the custard into individual dishes, sprinkle with brown sugar, and caramelize the top with a kitchen torch.