Milk infusion:
Pour the milk into a saucepan, add the cinnamon stick, vanilla and lemon zest.
Heat over medium heat and let boil for 5 minutes. Remove from heat and let steep for 10 minutes.
Preparation of egg yolks:
In a large bowl, beat the egg yolks with the sugar until smooth.
Dissolving cornstarch:
In a small bowl, mix the cornstarch with a little milk until completely dissolved.
Combination of mixtures:
Add the cornstarch mixture to the bowl containing the egg yolks and sugar, and mix well.
Milk filtration:
Strain the infused milk through a fine sieve directly into the bowl of egg mixture, then whisk until smooth.
Cooking the cream:
Pour the mixture into a saucepan over low heat, stirring constantly to prevent the cream from sticking to the bottom.
Thickening:
Continue cooking for about 10 minutes, until the cream thickens.
Mounting in the glasses:
Place 3 Maria biscuits in the bottom of 3 dessert glasses. Pour the cream into these glasses, then divide the rest of the cream into 3 other glasses.
Let cool, then place 3 Maria biscuits on the cream of the glasses without biscuits at the bottom.
Refrigeration:
Sprinkle with cinnamon and refrigerate for 4 hours.