To make the cake, pre-heat the oven to 180° and line 2x 30cm cake pans with baking paper.
Beat the butter and sugar together until light and fluffy.
In a separate bowl sift together the flour, baking powder, salt & cinnamon.
In a large measuring jug, beat together the milk, eggs, egg whites and vanilla.
Add the flour and liquid ingredients to the butter and sugar mixture, alternating between the two until all the ingredients have been incorporated and the batter is smooth.
Divide the mixture between the prepared cake pans and place in the oven.
Allow to bake for 30-35 minutes until a skewer inserted comes out clean. (If the cakes brown too much for your liking, simply cover loosely with some tin foil after 20 minutes of baking).
When the cakes are cooked, remove from the oven and allow to cool completely.
In the mean time, start with the custard filling.
Heat the milk, cream and butter in a medium saucepan.
In a bowl, whisk together the egg, egg yolks, cornflour, vanilla and sugar.
When the milk reached boiling point, remove from the heat and slowly whisk into the egg mixture.
Wipe the saucepan clean with a piece of kitchen paper and place on a low heat. Pour in the custard and continuously whisk/stir until the mixture forms a thick custard.
Allow to cook over low heat for 5-7 minutes whilst stirring until the mixture is smooth and thick and has no floury taste/texture.
Push the custard through a sieve into a clean bowl and cover with cling film (push the cling onto the surface of the custard). Place in the fridge and allow to cool completely.
To assemble the cake, pipe/spread 3/4 of the milk tart custard onto one of the cakes, top with the other cake.
Beat the cream until soft peaks form then fold into the remaining 1/4 of milk tart custard.
Top the cake with the whipped cream custard and sprinkle over some ground cinnamon.