Preheat oven at 150°C/300°F.

Sift the dry ingredients (flour and salt). Set aside.

Separate the eggs. One small bowl with yolk, a large bowl with the whites.

In a bowl, add the butter and milk over. Melt and heat up the 2 ingredients over a double boiler. Keep stirring until the butter is completely melted. The mixture will be well heated. Remove the bowl from the double boiler. Dry the bottom of the bowl with a cloth to prevent water dripping into the batter later. As the mixture is still hot, add it into the sifted dry ingredients. Use a whisk to mix them well until incorporated. The mixture will be thick as you mix.

Add in the vanilla extract.

Add in the yolks, one at a time. Mix until they are well combined. Set aside while working on the egg whites.

Mix the egg whites on low speed until foamy or bubbly. Add in the sugar in 3 batches. Continue mixing in medium speed. Mix until you achieve a smooth consistency. How you tell is simply lift up your mixer paddle, you will see a smooth tail hanging on the paddle. That is the time to stop.

Add a small portion of the egg whites into the yolk batter. Use a whisk to mix in a circular motion. Mix gently as we do not want to deflate the air in the egg whites. Transfer this yellow batter into the big portion of egg whites. Continue mixing with a whisk in a circular motion. Towards the end of mixing, switch it to a spatula to scrape the bottom and sides of the bowl to ensure well mixing and evenly.

Transfer the batter into a 7x7x3-inch pan, lined with non-stick parchment paper. I like using this reusable parchment paper, as it gives a nice and smooth sides. Normal parchment paper will usually turned out wrinkles on the sides.

Bake in preheated oven at 150°C/300°F for 55-60 min.

When the cake is done baking, immediately remove it from the pan and the parchment paper.

Cake can be served hot or when it’s completely cool down.