Heat the oven to 500°F (260°C). Lightly grease a 12-cup muffin tin.

Roll the thawed pastry into a tight log, cut into 12 equal rounds, and press each round into a muffin cup, spiraling the layers upward to form thin shells. Chill the tin while making the custard.

Warm the milk, cream, cinnamon stick, and lemon zest in a saucepan until steaming. Remove from the heat and steep for 5 minutes; discard the cinnamon and zest.

Whisk the sugar, egg yolks, cornstarch, vanilla, and salt until smooth. Slowly whisk in the warm milk mixture, then return it to the pan. Cook over medium-low heat, whisking constantly, until lightly thickened; do not boil. Strain and cool for 10 minutes.

Fill each pastry shell about three-quarters full. Bake 10 to 13 minutes, until the pastry is deeply golden and the custard has dark brown spots. Watch closely near the end.

Cool in the pan for 5 minutes, loosen carefully, and transfer to a rack. Serve warm or at room temperature with a little cinnamon.