Gather the ingredients.
Pour 5 cups of milk into a large saucepan. Add lemon peel and cinnamon stick and warm the milk, uncovered, over medium heat, until just before it boils. Remove from heat and allow to sit for 10 minutes.
In a small bowl, whisk remaining 1 cup milk with the cornstarch.
Place egg yolks in a large mixing bowl. Add the sugar and beat with an electric mixer until it is frothy.
Add the milk-cornstarch mixture and continue to beat with mixer until thoroughly mixed. Set aside.
Remove the lemon peel and cinnamon stick from the warm milk, using a slotted spoon.
Return the pot to the stove on medium heat. After milk is hot, but not boiling, add the vanilla extract .
Slowly pour egg yolk mixture into the warming milk, while beating with electric mixer on low speed.
Using a wooden spoon, stir continuously over medium heat, so the milk does not stick. Stir until mixture thickens.
Ladle thickened mixture through a fine mesh sieve placed over a large bowl, in order to eliminate any lumps.
Pour strained natillas mixture evenly into 6 small bowls, ramekins, or cups. Allow to cool to room temperature on the counter, then cover ramekins with plastic wrap and refrigerate until ready to serve.
Once chilled, garnish with cinnamon before serving.
