For green tea sponge cake: Mix egg yolks, sugar, water and cornoil together and stir till mixture is smooth.
Add in flour and green tea powder and mix evenly.
Whisk egg white with sugar till stiff peak. Fold in egg yolk mixture and pour mixture into a 9? square tin.
Bake at 170C for about 30 mins. or till skewer inserted comes out clean.
Leave cake to cool on wire rack and slice cake into 2 slices. Place 1 slice of cake into a 9? square cake ring.
Mousse: Heat milk till warm, then add in castor sugar and green powder. Stir till evenly mixed. Fold in egg yolks and stir. Becareful not to allow the egg yolk to overcook and it will become lumpy.
Add in melted gelatine mixture and leave to cool.
Fold in whipped cream gently.
Pour half of the mousse filling onto the prepared cake ring and then top up with the other slice of green tea sponge cake.
Pour balance mousse on top and level it evenly. Refrigerate till mousse is set.
Take out the cake from the cake ring and sieve green tea powder on top and decorate as desired