Melt chocolate in a double boiler and stir till smooth, set aside. (I microwaved the chocolate pieces for 45 seconds)

In a large bowl, beat egg lightly with a hand whisk, followed by oil, milk and melted chocolate, stir well.

Combine flour, cocoa powder, baking powder and baking soda together and sift into the egg yolk mixture, mix till combined and smooth to a thick paste.

Meringue - Whisk egg whites and cream of tartar at till foamy and gradually add in sugar and beat to stiff peak from medium to high speed.

Pour the batter into a 17cm chiffon pan and gently tap the pan on the table top to get rid of any trapped bubbles. Bake in preheated oven at 165C for about 40 minutes.

Invert cake pan immediately and let to cool down completely after baked.

Ganache Cream - Place chopped chocolate pieces and butter into a bowl. Bring whipping cream to a boil at medium heat, then pour over the chocolate pieces. Stir chocolate till smooth and add vanilla extract, stir well again. Leave chocolate cream to stand for 10 minutes before pouring on top of cake and spread evenly with a palette knife or a scraper. Refrigerate cake in the chiller for an hour before consuming.