Pre-heat oven to 165 deg C.  Prepare two 7-inch cake pans. Lightly grease only the base of the pans, but leave sides free of grease. If baking in a tube pan, do not line with baking paper or grease at all.

Onto a large baking sheet, sift a quantity of cake flour that is more than what you will need for the recipe. Then, turn up both opposite ends of the sheet, and while holding the flour steady in the trough, pour the required amount of sifted flour, measured here by weight, into a bowl large enough to hold the flour. This will ensure that you do not use more flour than is required.

Sift together the cake flour, cocoa powder, baking powder and salt into a bowl.

In a clean bowl or jug, combine the corn oil, cold water, chocolate emulco and vanilla extract, and stir thoroughly to mix well.

Using an electric mixer, place egg yolks and sugar into a mixing bowl.  Whisk on high speed until the yolks become light and fluffy (the yolks should triple in volume and turn a pale lemon colour).

Lower mixer speed to medium, and slowly pour the mixture from (3) in a steady continuous stream into the yolk mixture. Whisk together until just well blended.

Stop the mixer, and sift in the flour and cocoa mixture all at once. Turn the mixer on, on low speed this time, and whisk the flour into the yolk mixture until most of the flour has been incorporated.  Finish mixing by hand, using the whisk (detach from the mixer) or spatula to fold in all the flour until just well incorporated. Be careful not to over-mix or over-fold the mixture. Transfer to a clean bowl and set aside. Wash the mixer bowl and whisk attachment to remove all grease, and dry thoroughly.

In the cleaned mixer bowl, pour in the egg whites. Using the whisk attachment, beat at high speed. When the egg whites start to get foamy, add the cream of tartar.  About 30 seconds later, pour in the sugar in a steady continuous stream.  Continue beating until the egg whites reach the stiff peaks stage.

Add 1/3 beaten egg whites into the yolk mixture and mix using a spatula or hand whisk. Using quick but light moves, gently fold in the next 1/3, and then the last remaining 1/3.  Ensure that the egg whites are well incorporated with no visible streaks of unmixed whites in the mixture.  Be careful not to over-fold.

Tap the batter lightly on the counter top, before pouring into two 7-inch prepared round pans, with batter equally divided. Bake at the lowest rack in the oven for 25 minutes or until skewer inserted comes out clean. Immediately invert pan(s) onto a cooling rack for at least an hour before loosening cake. Cakes must be completely cooled before filling and frosting.

In an electric mixer, cream butter with the paddle attachment set on medium speed. Turn off the mixer. Sift confectioner's sugar and cocoa powder into the mixing bowl. Turn your mixer back on, set to the lowest speed (to avoid blowing out the powdered ingredients), until the sugar and cocoa has been incorporated into the creamed butter.

Tip: Add confectioner's sugar, half cup at a time, after the first cup has been incorporated, so that you can gauge how sweet you prefer your frosting.

Increase mixer speed to medium, and add vanilla extract, salt and cream. Continue beating for 3 minutes until creamed butter is light and fluffy. If your frosting needs a stiffer consistency, add a little more sugar. If your frosting needs to be thinned out, add additional cream or milk, 1 tbsp at a time, until desired consistency is reached. Set aside until ready to fill and frost the cakes.

On a cake turntable or large, round flat dish, place one cake layer (bottom side facing down) and centre it on the turntable or dish. Place two to three dollops of buttercream frosting on the cake layer.  Using an offset spatula, spread the cream into an even layer over the surface. Cover with the second cake layer on top of the cream, making sure that both layers align nicely all around the circumference of the cake. Frost all around the sides and the top of the cake with buttercream.  Smooth the sides and top with a broad spatula.  Decorate as desired.