The milk should be poured into the large saucepan. Uncover the pot, bring the milk to a simmer, and add the lemon peel and cinnamon stick. Take off the stove and set aside to cool for ten minutes.
Mix the cornstarch and the remaining 1 cup of milk in a small bowl.
Get a big bowl and add the egg yolks to it. Stir in the sugar and whip with a hand or stand mixer until foamy.
Combine the milk-cornstarch mixture and beat on low until combined. Put aside.
Using a slotted spoon, skim the lemon peel and cinnamon stick out of the hot milk.
Put the pot back onto the stove, but this time turn the heat down to medium. Add the vanilla extract once the milk is hot but not boiling.
To make a custard, add the egg yolk mixture to the warm milk slowly while whisking with a hand mixer or electric mixer on low speed.
Over medium heat, keep stirring with a wooden spoon to prevent the milk from scorching. Keep stirring until the liquid becomes thick.
Remove any clumps from the thickened mixture by ladling it through a fine mesh sieve set over a large bowl.
The custard should be strained through a fine metal sieve.
Divide the strained Natillas mixture among six individual serving bowls, ramekins, or cups. Place on a counter to cool to room temperature, then cover ramekins with plastic wrap and place in the fridge.
A dash of cinnamon on top before serving will make the dish even more delicious.