Preheat the oven to 325°F.
Separate the egg yolks and whites in two separate mixing bowls.
In the bowl with the yolks, add in HALF of the sugar and whisk until it becomes creamy and a light yellow colour. Set aside.
In the bowl with the whites, beat it with an electric hand held mixer to make meringue, while adding in the rest of the sugar little by little. Mix until stiff peaks form.
Add in the meringue to the yolk mixture in 2 separate times, while folding gently with a spatula.
Sift in the cake flour and fold it GENTLY until the flour has been incorporated.
In a small bowl, whisk together the melted butter (cooled), milk, and vanilla extract. Pour this around the edges of the cake batter in a circular motion.
Carefully fold the mixture. Do not overmix.
Pour into a 6” mold lined with parchment (do not grease the sides). Bang the pan on the counter for a few times to release all the air bubbles (too much air bubbles dries out the cake). Then put it in the preheated oven to bake IMMEDIATELY for 35-40 minutes.
Remove from the mold and transfer to a wire rack and remove the parchment. Cool to room temperature and then slice in equal layers. Enjoy!