Beat the sugar, eggs, salt and oil together till you get a frothy yet smooth consistency. You can use electric hand-beater/food processor or stand mixer for this operation.
Take a cup of flour and remove 2 tbsp from it. Then replace it with the corn flour. Add baking powder to this and sieve everything together nicely. This would mix the dry ingredients completely along with incorporating some air into it.
Add the dry ingredients to the beaten eggs. Put the vanilla extract into it once everything is mixed nicely. If you find the batter too tight, then you may add some milk to it. Add 1 tbsp. at a time so that the batter does not get too runny!
It is always good to let the batter rest for a minute or two before it is poured into the mold. During this time grease and dust the baking dish.
Now, pour the batter in. Check if there are any air bubbles on the surface of the cake. Pop them if you find any. For a microwave oven, it should take 4 minutes to cook at high power. If you have an OTG, then on bake mode, it should be done in 20 minutes.
Once you see the cake shrinking inside the mold, you know that it is ready. Still to be sure, poke a skewer in the center to check. It should come clean. If you find it wet, then prolong the cooking by few minutes, keeping an eye on the cake. When you find the cake done, take it out and let it cool on a wire rack.
Slice the vanilla cake horizontally and make 3 tiers.
Now, whisk the whipping cream till soft peaks. Add the Dulce de Leche in it and whip it till you see stiff peaks.
Now, start assembling the cake on your cake table. Take the bottom layer and spread some Dulce de Leche on it first. Then take some of the whipped cream and spread it gently covering the base layer of the cake evenly.
On the top of it, place the second layer of the cake and repeat. Once you stack the third layer, crumb coat the cake with little cream and place it the freezer for 15-20 minutes. Meanwhile, put the whipped cream in the freezer as well. This would stop it from melting.
After that, put the final coat of whipped cream on the cake. Cover the top as well as the sides of it and make it look as even as possible.