Prepare an 18cm bottom-removable round cake pan and cover the inside with parchment paper (If you don't have parchment paper, you can use regular paper).

Whisk together the flour, cocoa powder and baking powder and sift. Set aside until use.

Beat the egg yolk in a medium mixing bowl. Add the vanilla essence and milk and whisk well.

With an electric mixer fitted with a wire whip, beat the egg whites on high speed in a large mixing bowl. Add the sugar gradually and whip until the mixture is fluffy and stiff. Change the mixer speed to medium and keep mixing for 1 min (to equalize the size of bubbles). Move to a large mixing bowl.

Pour the egg yolk mixture into the whipped egg whites (meringue) and mix with a spatula until half-mixed.

Add the flour mixture to the wet mixture and mix with a spatula until you can't see the flour any more.

Add the vegetable oil to the mixture and mix well.

Heat a large skillet at low temperature and coat with butter. Place the sponge cake pan upside down into the skillet. Pour the mixture into the mold and cover the mold with a lid. Cook for 35 min or until bubbles appear on the surface.

Remove the cake pan and parchment paper. Flip the pancake with a spatula to cook the other side.

Serve with whipped cream, fruits, chocolate sauce etc...