[Prepare the utensils] You will need a large bowl, hand mixer, cake mould (line with baking paper. If you use a paper mould use as it is), frying pan, flour sifter and plastic spatula.
[Prepare the ingredients] Put the eggs in a large bowl. Measure the flour and sugar with cling film on a scale. Put the butter, milk and vanilla oil in a sauce pan over bain-marie.
[The last preparation] Fill the frying pan with water and put over heat. Pre-heat the oven to 180°C.
Beat the eggs in a large bowl lightly with hand mixer. Add the granulated sugar in one go and start to beat at high speed.
Check if the water in the frying pan is warm enough to have little bubbles on the surface. Turn off the heat and place the large bowl over the warmed water. Continue to beat with hand mixer over bain-marie.
After the mixture is slightly warm to the touch remove the bowl from the hot water. When you touch the mixture with your clean finger and it doesn't feel cold, it is about right.
Place a pan with butter in the hot water in the frying pan to melt.
Tilt the large bowl and continue to beat with hand mixer. You need to move your hand mixer time to time and rotate your bowl.
Continue to beat to make the batter voluminous with plenty of air.
When you lift the hand mixer and try to draw 8 on the surface a clear 8 remains on the surface for a few seconds it is ready.
Stir the mixture gently at low speed for 1 minute and stabilize and smooth out the texture.
Hold the flour sifter up above the bowl and sift the flour again evenly onto the surface of the mixture. If you don't the weight of the flour pushes out the air of the mixture.
Fold in several times with a plastic spatula. Stop folding in when you see the flour partially combined. Do not over-mix.
After melting the butter over a bain-marie, stir in a few drops of vanilla oil and a spoonful of the sponge batter. Mix well to ensure the butter and batter are thoroughly mixed in.
Add the mixture from Step 14 into the large bowl. To avoid the heavy butter mixture from damaging the airy sponge batter pour the butter mixture onto the spatula and drizzle over the butter mixture evenly. After adding, fold in several times as you did at Step 13. Stop folding in once it's evenly mixed! Do not over-mix!!
The sponge batter is done. Pour the batter into the mould and give several taps to get rid of excess air. Bake in the oven pre-heated to 180°C for 16 to 18 minutes.
When a skewer inserted in the middle and comes out clean, it is ready. Remove the sponge from the mould and peel off the baking paper. Leave to cool.
If you have corn flour use 50 g of plain flour and 10 g of corn flour. You will have a more delicate texture.
Story Behind this Recipe
After many trials I have learned some key points. I recommend this recipe to my friends. This is a perfect recipe I am proud of.
The most important key is to make the mixture voluminous with air before adding the flour. I have never failed to make nice sponge by doing this, so this is important. After adding the flour try not to damage the airy mixture. Fold in carefully and quickly. After butter mixture is combined evenly stop folding in!