Preheat your oven to 180 degrees (conventional oven) and line the bottom of two x 20cm round cake tins with baking paper and lightly grease the sides.
Sift the cornflour, self raising flour and cocoa into a bowl and set aside until needed.
Using an electric mixer, beat the eggs, caster sugar and vanilla for approximately 8 - 10 minutes until the mixture is thick and pale yellow.
Working quickly, sift the dry ingredients again over the the top of the egg and sugar mixture, add the milk and gently fold the ingredients through to combine.
Spoon the chocolate sponge cake mixture evenly between the prepared tins and bake for 18 - 20 minutes in your preheated oven until the chocolate sponges have risen and began to shrink away from the sides.
Carefully remove the cake tins from the oven and let the sponges cool in the tins for 10 minutes before carefully turning out onto a wire rack to cool completely.
Once your chocolate sponges have completely cooled, combine the thickened cream, vanilla essence and icing sugar in a bowl and whisk until soft peaks form.
Spread approximately ¾ cup of whipped cream on top of one chocolate sponge before carefully adding the second sponge on top of it. Cover with whipped cream and decorate with the chopped Tim Tams.