Peel the Clementine (1) and reserve the peel. Slowly bring Milk (4 cup), Clementine Peel, Cinnamon Stick (1) and Salted Butter (1 tablespoon) to a boil.
While the milk mixture is coming up to a boil, whisk the Caster Sugar (1 cup) and Egg (3) together.
Add the All-Purpose Flour (2 tablespoon), Salt (1 pinch) and Corn Flour (2 tablespoon) to the egg mixture, whisk well until all combined.
When the milk mixture has come up to a boil, remove from the heat and add a small amount to the egg and sugar mixture. Whisk well and continue adding milk to the egg mixture, until everything is combined into a thin custard.
Pour the custard mixture back into the pot, and place back on a low heat.
Continue to whisk, making sure to cook slowly until the custard mixture has thickened. This should take about 10 minutes. Remove from the heat.
Bake the Frozen Shortcrust Pastry (1) according to package instructions and let cool on a tray.
Pour the cooked custard into the pastry shell.
Dust with Ground Cinnamon (1 tablespoon).
Place in the refrigerator to set for a minimum of two hours. Serve and enjoy!