Combine the crushed Tennis biscuits with the melted butter until evenly coated.
Spoon about 1 tablespoon of the biscuit mixture into the bottom of each shooter glass and press down lightly.
In a saucepan, heat the milk and cream until just below boiling.
In a separate bowl, whisk together the sugar, cornflour, cake flour, and egg yolks until smooth.
Gradually whisk a little of the hot milk into the egg mixture to temper it.
Pour the mixture back into the saucepan and cook over medium heat, stirring constantly until thick and smooth.
Remove from the heat and stir in the butter and vanilla essence.
Allow the filling to cool slightly, then spoon or pipe it over the biscuit bases.
Refrigerate for at least 2 hours until fully chilled.
Before serving, dust generously with ground cinnamon and garnish with whipped cream or extra biscuit crumbs if desired.