Preheat oven to 180 °C (350°F) conventional (see note 2 if using a convection oven with a fan) and lightly grease only the bottom of a 9x13 inch cake pan. Leave the sides of the pan ungreased and do not line them (see note 3).

Sift together flour, cornstarch, baking powder and salt. Mix until well combined and set aside.

In a medium sized bowl add in egg whites and using a hand or stand mixer, whip on a medium high speed for 30 seconds until foamy (see note 4). Once foamy, gradually add in ½ a cup (100g) of the sugar and then continue mixing until you reach stiff peaks (this should take about 3-4 minutes). Set aside.

In a large bowl add in the remaining ½ cup (100g) of white sugar and warm water. Mix so that the sugar is coated in the water. Add in the egg yolks and vanilla, and with a hand or stand mixer, whip on a medium high speed for 2 minutes until the yolks are pale and slightly thickened.

Stream the vegetable oil into the egg yolk mixture while mixing on a medium speed. Mix until well combined.

Add in half of your egg whites to your egg yolk mixture, and using a spatula gently fold until just combined - do not overmix. Next add in the sifted dry ingredients from earlier and fold until just combined. Finish off by adding in the remaining egg whites and fold until just combined. You can use your spatula to break up any large chunks of unmixed egg whites by pushing them gently up against the sides of the bowl, but try not to push out too many of the air bubbles and do not overmix.

Distribute the batter evenly into the prepared cake pan. Drop the cake tin lightly on the counter twice to remove any large air bubbles and bake for 25 minutes. To test whether the cake is done, gently touch the top and it should create a little indent which slowly bounces back.

Once the sponge is done, immediately drop the cake tin on your counter from a height of about 10cm to help release some of the steam, and then turn it upside down (while still in the baking tin) on a wire rack to cool for 30 minutes (see note 5).

In a jug (or something that will allow you to easily pour the milk) combine the evaporated milk, condensed milk and heavy cream.

Once the cake has been cooling for 30 minutes, turn it upright and run a knife along the edges of the cake tin to release the cake from the sides. Use your fingers to gently rub off the top layer of brown 'skin' on the sponge (see video for demonstration). Once the top is removed, use a fork to poke holes all over the top of the cake (only poke about ¾s of the way into the cake - not all the way to the bottom).

NOTE FEOM REDDITOR

For the milk I heated up a small can of condensed milk and a bigger can of evaporated milk with some cardamom. Poured that in after cooling.

For the top I just whipped up some double cream and icing sugar then topped with some crushed pistachios!

Pour the milk mixture evenly over the top of the cake. Try and do this as evenly as possible and make sure the entire top of the cake is soaked in milk, including the edges.

Cover with cling wrap and place into the fridge to rest for a minimum of 2 hours (ideally overnight if you have the time).

Once the cake is ready to be served, prepare the whipped cream frosting.

In a large bowl, combine the mascarpone, powdered sugar and vanilla. Mix on a low speed for 10 seconds, and then turn up the speed to a medium high and mix until well combined. If using a stand mixer use the whisk attachment.

Add in the heavy cream and mix on a low speed for 10 seconds (to allow everything to combine without the cream splattering), and then turn up the speed to a medium high and whip until you reach stiff peaks. Keep a careful eye on the mixture as you don't want to overwhip the cream.

Spread the whipped cream out evenly over the top of the cake, and sprinkle some cinnamon on the top using your fingers - you don't want too much cinnamon. Slice and serve as is or with fresh fruit!