Natillas (Spanish Custard)

Pour the milk into a saucepan and add the cinnamon stick, vanilla, and lemon rind. Warm it over medium heat until it reaches a gentle boil, then let it bubble for about 5 minutes. Remove it from the heat and allow the mixture to steep for 10 minutes so the flavors fully infuse.
In a large bowl, whisk the egg yolks with the sugar until well combined.
In a small bowl, dissolve the cornstarch in the 20 ml of milk until completely smooth. Pour this mixture into the bowl with the yolks and sugar, whisking until fully combined. Strain the infused milk through a fine mesh sieve into the yolk mixture and whisk again until the custard base is silky and smooth.
Pour the mixture back into a clean saucepan and cook over low heat, whisking constantly until it thickens, about 10 minutes.
Place three Maria cookies at the bottom of each dessert glass. This is optional, but it adds a lovely touch, feel free to use any tea biscuits you like instead.
Divide the custard evenly among the 6 glasses, filling both the ones with cookies at the bottom and the plain ones. Place a Maria cookie on top of the custard in the glasses that don’t already have one, then sprinkle each with a light dusting of cinnamon. Refrigerate for 4 hours, or until well chilled and set.