In a medium saucepan, bring the milk, lemon and orange peel, and cinnamon stick to a simmer over low heat. Stir occasionally to prevent it from sticking and burning. Remove from heat and let it steep, covered, for 30 minutes. Strain using a fine mesh sieve to remove the peels and cinnamon stick.

In a separate bowl, whisk egg yolks and sugar until the mixture becomes pale and smooth, about 1 minute. Add the cornstarch to the mixture and incorporate using a whisk until fully combined. 

Gradually add the egg mixture to the warm milk, whisking constantly to prevent the eggs from scrambling. 

Once the mixture is fully incorporated, stir over low heat until it thickens to a pudding-like consistency, about 7 minutes. Don't let the custard boil, or it will curdle.

Remove from heat and strain the custard again, before pouring into ramekins or clay pots. Cover with plastic wrap, pressing directly unto the surface to prevent from forming a thick skin. Let them cool, covered, and then refrigerate for 4 hours but preferably overnight.

To serve, sprinkle about 1 teaspoon of granulated sugar on top and caramelize using a kitchen blowtorch.