Crush the Mari biscuits in a food processor until they are finely ground and free of lumps.
Combine the crushed biscuits with melted butter and mix until all the crumbs are evenly coated.
Press this mixture firmly into a springform pan, covering the base and about three-quarters of the way up the sides. Use a ramekin to smooth the edges.
Refrigerate the crust while you prepare the filling.
In a pot, combine the milk, butter, and vanilla, and gently heat the mixture.
In a separate bowl, whisk together the eggs and egg yolks with the sugar until well combined.
Gradually pour the warm milk mixture into the egg mixture, then add the flour and cornflour, mixing until smooth.
Return the combined mixture to the pot and cook over medium heat, stirring continuously until it thickens and becomes creamy.
In a clean bowl, beat the egg whites until stiff peaks form, then gently fold them into the custard mixture.
Pour the custard over the prepared biscuit base and smooth the top.
Place the tart in the refrigerator to set.
Once set, place a template over the custard and dust with cinnamon. Carefully remove the template.
Remove the ring from the springform pan, slice the tart, and enjoy.
