This is a recipe inspired by the Portuguese "Pasteis de Nata" (translation: fresh cream tiny cakes). One can find them everywhere in Portugal, but the most famous are the "Pasteis de Belem" that you can only taste in Belem, Lisbon. This is our recreation of the recipe.
Preheat oven to 375 degrees F. Lightly grease 12 muffin cups with butter. Cover each of the muffin cups with the puff pastry (use a large mug to cut the puff pastry sheets into circles).
In a saucepan put the milk with sugar, lemon and cornstarch (when adding the cornstarch stir energetically and constantly to avoid lumps). Before it starts boiling, reserve ¼ cup of the milk mixture in a cup (this will be used later to temper the egg yolks). Let it cook in medium-low, stirring constantly, until the mixture thickens. Remove the lemon rind.
Beat the egg yolks in a different bowl. Then add the ¼ cup of the milk mixture that we saved earlier, whisking constantly. Add this into the saucepan with the rest of the mixture while whisking energetically. Do this for 5 minutes or until it is thickened.
Fill 2/3 of the pastry-lined muffin cups with the egg custard and bake them in a preheated oven for 20-25 minutes, or until crust is golden brown.
Serve warm or cold. Add a dash of ground cinnamon and/or powdered sugar on top. Enjoy!