Place the milk, cinnamon stick, salt and lime peel in a heavy saucepan and bring to a boil. Remove from the heat and allow to cool, letting the spice and lime steep in the milk.
In a bowl, beat the egg yolks with the sugar and the dissolved cornstarch until blended well.
Discard the cinnamon stick and lime peel and combine the infused milk with the egg yolks in a heavy saucepan over medium heat, stirring constantly. When the mixture thickens to soft-custard consistency, turn the heat off and add the vanilla. Pour into a large dessert dish (like a 7-inch souffle dish) or 4 individual 1/2-cup dessert ramekins and chill.
Serve sprinkled with ground cinnamon.
2 cups milk
1 stick cinnamon
1 quarter-size piece of lime peel
4 egg yolks
1/2 cup sugar
2 tablespoons cornstarch dissolved in 1/8 cup water
Scrapings of 1/4 vanilla bean, or more to taste
Ground cinnamon, for garnish