Steps
1. Preheat the oven to 180°C (350°F).
2. Crush the digestive biscuits into fine crumbs.
3. Melt the margarine and mix it with the biscuit crumbs.
4. Press the mixture into the bottom of a tart pan to form the crust.
5. In a saucepan, heat the milk until almost boiling.
6. In a separate bowl, whisk together the sugar, cornstarch, eggs, and vanilla extract.
7. Slowly pour the hot milk into the egg mixture while continuously whisking.
8. Return the mixture to the saucepan and cook over medium heat, stirring constantly, until thickened.
9. Pour the filling into the prepared crust.
10. Bake for 20-25 minutes, or until the filling is set.
11. Allow the tart to cool completely before refrigerating for at least 2 hours.
12. Sprinkle with ground cinnamon before serving.