Found the recipe from Alex Goh from the internet, I do some adjustment to the recipe. Yumm, so soft like cotton.
COTTON SPONGE CAKE
60g butter, melted ( I used vegetable oil)
80g flour ( I added 4 tbs corn four)
80ml UHT milk
1 egg +5 egg yolks
5 egg whites
Pinch of salt ( I used cream of tartar)
1. Beat 1 egg plus 5 yolks until creamy and fluffy. Fold in flour and alternate it with milk. Add in melted butter and mix well.
2. Whip egg whites with a pinch of salt and sugar until soft peak.
3. Mix step (2) above with egg yolk batter till well combined.
4. Pour into fully lined baking pan (mine is 8" square).
5. Bake at preheated oven 170 deg C for 25 mins then reduce heat to150 deg C for another 10 mins or till done.
6. Let the cake sits for 2 mins and unmould it.