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).

Beat the egg yolk in a medium mixing bowl. Add the vanilla essence and milk and mix 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 3 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 stir until half-mixed.

Add the flour mixture to the wet mixture and stir with a rubber 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, maple syrup, etc...