Prepare the Egg Yolks: In a medium bowl, whisk together the egg yolks, 30 grams of sugar (half of the sugar), milk, and vegetable oil until smooth and pale yellow. Make sure everything is well combined. This mixture will be the base of our cake, giving it richness and flavor.

Add Vanilla and Flour: Stir in the vanilla extract to the yolk mixture. Gradually sift in the cake flour into the bowl. Gently fold the flour into the wet ingredients until just combined. Be careful not to overmix at this stage – we want to keep the batter light. Set this bowl aside for now.

Whip the Egg Whites: In a clean, grease-free large bowl, add the egg whites and cream of tartar. Beat with an electric mixer on medium speed until soft peaks form. Soft peaks mean that when you lift the whisk, the peak of the egg white will gently fold over.

Sweeten the Meringue: Gradually add the remaining 30 grams of sugar to the egg whites, one tablespoon at a time, while continuing to beat on medium-high speed. Continue beating until stiff peaks form. Stiff peaks mean that when you lift the whisk, the peak of the egg white stands straight up and doesn't fold over. Be careful not to overwhip, or the meringue will become dry.

Combine the Batters: Take a large spoonful of the meringue and gently fold it into the egg yolk batter. This will lighten the yolk batter and make it easier to incorporate the rest of the meringue. Then, gently fold the remaining meringue into the yolk batter in two additions. Fold until just combined and you see no streaks of egg white. Again, be gentle and avoid overmixing to keep the cake fluffy.

Prepare the Pan: Preheat your oven to 300°F (150°C). Grease and flour a 6-inch round cake pan, or line the bottom with parchment paper. Using a pan with higher sides is recommended to allow the cake to rise properly.

Pour and Bake: Pour the batter into the prepared cake pan. Gently tap the pan on the counter a few times to release any large air bubbles. Place the cake pan in a larger baking pan and add hot water to the larger pan, creating a water bath that comes about halfway up the sides of the cake pan. This water bath helps the cake bake evenly and stay moist.

Bake the Cake: Bake in the preheated oven for 60-70 minutes, or until a toothpick inserted into the center comes out clean. The baking time may vary slightly depending on your oven, so keep an eye on it. The cake should be golden brown on top.

Cool and Unmold: Once baked, turn off the oven and leave the oven door slightly ajar for about 10 minutes. This gradual cooling prevents the cake from collapsing. Then, remove the cake from the oven and let it cool in the pan for another 10 minutes before gently inverting it onto a serving plate to cool completely. If you lined the pan with parchment paper, it should come out easily.